Multipoint control method, apparatus and program

ABSTRACT

A technique is provided that can reduce degradation of the sound quality due to a tandem connection of paired coding and decoding, and can reduce the operation processing amount and the required memory amount of a multipoint control unit. In multipoint connection between terminals of a plurality of communication networks (for example, a fixed phone line and a mobile phone line) having different communication capacities, when a multichannel coding including a monaural coding scheme of a communication network having a smaller communication capacity is used in a communication network having a larger communication capacity to transmit sounds of a plurality points to the communication network terminal having the larger communication capacity, control is exercised such that monaural codes of the plurality points are output.

TECHNICAL FIELD

The present invention relates to at least one of a control technique ina multipoint control unit (MCU) for a multipoint phone conference, acoding technique of a sound signal at each point, and a decodingtechnique of a sound signal at each point.

BACKGROUND ART

The technique disclosed in Patent Literature (PTL) 1 is known as arelated technique for the control in a multipoint control unit formultipoint phone conferencing, coding of sound signals at each point,and decoding of sound signals at each point. The technique disclosed inPTL 1 uses embedded coding through basic quality coding and qualityextension coding. The sound signal coding apparatus at each pointobtains a code by performing embedded coding through basic qualitycoding and quality extension coding on input sound signals, and outputsthe code to the multipoint control unit. For a basic quality codingpart, the multipoint control unit obtains sound signals by decoding thecodes of all points, mixes the obtained sound signals, codes the mixedsound signal, and outputs a code obtained from the mixed sound signal toeach point. On the other hand, for a quality extension coding part, themultipoint control unit (a) selects a code of one most important pointso as to send the code to each point; or (b) obtains sound signals bydecoding codes of a plurality of highly important points, mixes theobtained sound signals, codes the mixed sound signal and outputs thecode obtained from the mixed sound signal to each point. A sound signaldecoding apparatus of each point obtains a sound signal including thebasic quality part of all points and the quality expansion part of thehighly important point by decoding the code output by the multipointcontrol unit.

CITATION LIST Patent Literature

PTL 1 JP 2005-229259 A

SUMMARY OF THE INVENTION Technical Problem

In the technique disclosed in PTL 1, the basic quality part isnecessarily decoded at the multipoint control unit before it is coded,and the paired coding and decoding are connected in tandem. Thus, whenthe technique disclosed in PTL 1 is implemented using a coding anddecoding scheme used in mobile communication that entails highcompression, a large operation processing amount and a large memoryamount, the sound quality may be significantly degraded due to thetandem connection of paired coding and decoding, and the operationprocessing amount and the required memory amount of the multipointcontrol unit may be increased due to a large number of decodingprocesses and coding processes.

Means for Solving the Problem

A multipoint control method according to an aspect of the presentinvention is a method in a multipoint control unit to which one or morefirst communication network terminal apparatuses and one or more secondcommunication network terminal apparatuses are connected through acommunication path, the number of points at which the one or more firstcommunication network terminal apparatuses are located being M (M is aninteger of 1 or greater), the number of points at which the one or moresecond communication network terminal apparatuses are located being N (Nis an integer of 1 or greater, and M+N is 3 or greater), the methodincluding: a point selecting step of, for a predetermined time period,selecting, by the multipoint control unit, one point or two points fromamong M points at which the one or more first communication networkterminal apparatuses are located and N points at which the one or moresecond communication network terminal apparatuses are located, a bitstream input from each first communication network terminal apparatus tothe multipoint control unit through the communication path being a bitstream including, as codes representing a sound signal, a monaural codeCFM_(m) (m is an integer from 1 to M) obtained by coding a mixed signalof sound signals of two or more channels input to the firstcommunication network terminal apparatus by a first coding scheme and anextension code CFE_(m) including a code representing informationcorresponding to a difference between the input sound signals of two ormore channels, and a bit stream input from each second communicationnetwork terminal apparatus to the multipoint control unit through thecommunication path being a bit stream including, as a code representinga sound signal, a monaural code CMM_(n) (n is an integer from 1 to N)obtained by coding a sound signal of one channel input to the secondcommunication network terminal apparatus by the first coding scheme; anda bit stream generating step of, when a single first communicationnetwork terminal apparatus of an M₁-th point (M₁ is an integer from 1 toM) and a single second communication network terminal apparatus of anN₁-th point (N₁ is an integer from 1 to N) are selected from the one ormore first communication network terminal apparatuses and the one ormore second communication network terminal apparatuses, generating andoutputting, by the multipoint control unit, as a bit stream for anunselected first communication network terminal apparatus of the one ormore first communication network terminal apparatuses that is located ata point that is not selected in the point selecting step, a bit streamincluding, as codes representing a sound signal, a monaural codeCFM_(M1) of codes representing a sound signal of the M₁-th point and amonaural code CMM_(N1) that is a code representing a sound signal of theN₁-th point.

Effects of the Invention

According to the present invention, even when a high-compression codingscheme such as that used in mobile communication is used forimplementation, degradation of the sound quality due to a tandemconnection of paired coding and decoding can be reduced, and theoperation processing amount and the required memory amount of themultipoint control unit can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of a multipoint phoneconnection system.

FIG. 2 is a block diagram illustrating an example of a fixedcommunication terminal apparatus.

FIG. 3 is a block diagram illustrating an example of a mobilecommunication terminal apparatus.

FIG. 4 is a block diagram illustrating an example of a multipointcontrol unit.

FIG. 5 is a diagram schematically illustrating an example of a codestring representing a sound signal when selection point information isinformation of case 1.

FIG. 6 is a diagram schematically illustrating an example of a codestring representing a sound signal when selection point information isinformation of case 2.

FIG. 7 is a diagram schematically illustrating an example of a codestring representing a sound signal when selection point information isinformation of case 3.

FIG. 8 is a diagram schematically illustrating an example of a codestring representing a sound signal when selection point information isinformation of case 4.

FIG. 9 is a diagram schematically illustrating an example of a codestring representing a sound signal when selection point information isinformation of case 5.

FIG. 10 is a flowchart of an example of a process of a sound signalfixed transmission side unit of the fixed communication terminalapparatus.

FIG. 11 is a flowchart of an example of a process of a sound signalfixed reception side unit of the fixed communication terminal apparatus.

FIG. 12 is a flowchart of an example of a process of a sound signalfixed transmission side unit of the mobile communication terminalapparatus.

FIG. 13 is a flowchart of an example of a process of a sound signalfixed reception side unit of the mobile communication terminalapparatus.

FIG. 14 is a flowchart of an example of a process of the multipointcontrol unit.

DESCRIPTION OF EMBODIMENTS

As illustrated in FIG. 1, a multipoint phone connection system 10includes a multipoint control unit 100, a first communication networkterminal apparatus 200-m (m is an integer from 1 to M), and a secondcommunication network terminal apparatus 300-n (n is an integer from 1to N). The multipoint control unit 100 and each first communicationnetwork terminal apparatus 200-m are connected to each other througheach transmission path 400-m of a first communication network. Themultipoint control unit 100 and each second communication networkterminal apparatus 300-n are connected to each other through eachtransmission path 500-n of a second communication network. The firstcommunication network and the second communication network arecommunication networks that differ from each other in the communicationcapacity for real-time transmission. The communication capacity of eachtransmission path 400-m of the first communication network in eachdirection is equal to or greater than K times (K is an integer of 2 orgreater) the communication capacity of each transmission path 500-n ofthe second communication network in each direction, and the total numberof the first communication network terminal apparatuses and the secondcommunication network terminal apparatuses is K+1 or greater. The K+1 orgreater terminal apparatuses include at least one first communicationnetwork terminal apparatus and at least one second communication networkterminal apparatus, and each terminal apparatus can playback decodedsound signals corresponding to sound signals of terminal apparatuses atup to K points. That is, in the present invention, it suffices M≥1, N≥1,and M+N≥K+1. In the present invention, there is no limitation on whethereach communication network is fixed communication or mobilecommunication, or in other words, whether the transmission path of eachcommunication network is a wired transmission path or a wirelesstransmission path, and the like.

The present invention is also applicable to a case where the firstcommunication network is an existing fixed phone communication networkand the second communication network is an existing mobile phonecommunication network, for example. In view of this, for ease ofunderstanding, the following embodiments are described with an examplein which the first communication network is assumed to be an existingfixed phone communication network and the second communication networkis assumed to be an existing mobile phone communication network, or morespecifically, an example in which the first communication networkterminal apparatus 200-m is a fixed communication terminal apparatus200-m, the second communication network terminal apparatus 300-n is amobile communication terminal apparatus 300-n, the transmission path400-m of the first communication network is a fixed transmission path400-m, and the transmission path 500-n of the second communicationnetwork is a mobile transmission path 500-n, as illustrated in FIG. 1.

FIRST EMBODIMENT

First, a configuration of a multipoint phone connection system and eachapparatus included in the multipoint phone connection system in a firstembodiment are described.

Multipoint Phone Connection System 10

As illustrated in FIG. 1, the multipoint phone connection system 10according to the first embodiment includes the multipoint control unit100, a plurality of (M) fixed communication terminal apparatuses 200-m(m is an integer from 1 to M), and a plurality of (N) mobilecommunication terminal apparatuses 300-n (n is an integer from 1 to N).In the present embodiment, descriptions will be made on the assumptionthat two or more fixed communication terminal apparatuses 200-m and twoor more mobile communication terminal apparatuses 300-n are provided.That is, in the present embodiment, M is an integer of 2 or greater, andN is an integer of 2 or greater. The multipoint control unit 100 andeach fixed communication terminal apparatus 200-m are connected to eachother through each fixed transmission path 400-m having a communicationcapacity sufficient for performing the real-time transmission of a codeequivalent to one channel of a coding scheme of a phone band voice for afixed phone, such as a transmission path for a voice line of a fixedphone of 64 kbps in each of up and down directions, for example. Thecoding scheme of a phone band voice for a fixed phone is ITU-T G.711,for example The multipoint control unit 100 and each mobilecommunication terminal apparatus 300-n are connected to each otherthrough each mobile transmission path 500-n having a communicationcapacity sufficient for real-time transmission of a code equivalent toone channel of a coding scheme of a phone band voice for a mobile phone,such as a transmission path for a voice line of a mobile phone of 13.2kbps in each of up and down directions, for example. The coding schemeof a phone band voice for a mobile phone is 13.2 kbps mode of 3GPP EVSstandard (3GPP TS26.442), for example.

Fixed Communication Terminal Apparatus 200-m

The fixed communication terminal apparatus 200-m is an advanced phone ora PC provided with a microphone and a speaker, and includes a soundsignal fixed transmission side unit 210-m and a sound signal fixedreception side unit 220-m as illustrated in FIG. 2, for example. Thesound signal fixed transmission side unit 210-m includes a sound pickupsection 211-m, a coding section 212-m and a control information grantingsection 213-m. The sound signal fixed reception side unit 220-m includesa control information analysis section 221-m, a decoding section 222-mand a playback section 223-m.

The sound signal fixed transmission side unit 210-m of the fixedcommunication terminal apparatus 200-m performs the processes of stepS211 to step S213 exemplified in FIG. 10 and the following description,and the sound signal fixed reception side unit 220-m of the fixedcommunication terminal apparatus 200-m performs the processes of stepS221 to step S223 exemplified in FIG. 11 and the following description.

Sound Signal Fixed Transmission Side Unit 210-m

For example, for each predetermined time period of 20 ms, that is, foreach frame, the sound signal fixed transmission side unit 210-m obtainsa fixed terminal sending bit stream that is a bit stream including acode corresponding to digital sound signals of two channels, and outputsthe bit stream to the fixed transmission path 400-m. Specifically, thesound signal fixed transmission side unit 210-m outputs a fixed terminalsending bit stream to the multipoint control unit 100 through the fixedtransmission path 400-m.

Sound Pickup Section 211-m

The sound pickup section 211-m of the sound signal fixed transmissionside unit 210-m includes two microphones and two AD conversion sections.The microphones and the AD conversion sections are associated with eachother in a one-to-one relationship. The microphone picks up a soundgenerated in a spatial region of around the microphone, converts thesound into an analog electric signal, and outputs the analog electricsignal to the AD conversion section. The AD conversion section convertsan input analog electric signal into a digital sound signal as a PCMsignal having a sampling frequency of 8 kHz, for example, and outputsthe signal. Specifically, the sound pickup section 211-m outputs digitalsound signals of two channels corresponding to sounds picked up by thetwo microphones, such as digital sound signals of a two-channel stereoof left and right channels, to the coding section 212-m of the soundsignal fixed transmission side unit 210-m (step S211).

Coding Section 212-m

For each frame, the coding section 212-m of the sound signal fixedtransmission side unit 210-m obtains a monaural code that is a coderepresenting a mixed signal of digital sound signals of two channelsinput from the sound pickup section 211-m, and an extension code thatcan represent the input digital sound signals of two channels when theextension code is used in addition to the monaural code and

the obtained monaural code and the obtained extension code are output tothe control information granting section 213-m of the sound signal fixedtransmission side unit 210-m (step S212). Specifically, the extensioncode obtained by the coding section 212-m is the code whereby any of thedecoded digital sound signals of the two channels cannot be obtainedwhen only the extension code is used, the code whereby both of thedecoded digital sound signals of the two channels can be obtained whenthe code is used together with the monaural code, and the code thatincludes a code representing information corresponding to a differencebetween the input digital sound signals of two channels.

The mixed signal of digital sound signals of two channels is forexample, a sequence obtained by adding together samples corresponding todigital sound signals of two channels, a sequence obtained by averagingsamples corresponding to digital sound signals of two channels, asequence obtained by adding together or averaging digital sound signalsof two channels at least one of which is deformed or delayed, a sequenceobtained by deforming the above-described sequences obtained through theadding or averaging, or the like, and is a signal corresponding to a sumof digital sound signals of two channels.

The code representing information corresponding to a difference betweendigital sound signals of two channels is a code obtained by codinginformation of a waveform representing a difference between digitalsound signals of two channels, a code representing a feature parameterrepresenting a difference between digital sound signals of two channels,or the like. Information of a waveform representing a difference betweendigital sound signals of two channels is, for example, a sequence of avalue obtained by subtracting the sample corresponding to the digitalsound signal of one channel from the sample of the digital sound signalof the other channel, a sequence of a value obtained by dividing, by 2,a value obtained by subtracting the sample corresponding to the digitalsound signal of one channel from the sample of the digital sound signalof the other channel, a sequence obtained through the subtraction, orthe subtraction and division, of digital sound signals of two channelsat least one of which is deformed or delayed, a sequence obtained bydeforming the sequence obtained through the subtraction, or thesubtraction and division, a part of the above-described sequences. Thefeature parameter representing a difference between digital soundsignals of two channels is one or more feature amount representing arelationship or a degree of difference between the signals of thechannels, such as a difference in energy of each frequency band, acorrelation of each frequency band, and a phase difference of eachfrequency band of the digital sound signals of two channels.

More specifically, for each frame, the coding section 212-m obtains amonaural code by coding a mixed signal of digital sound signals of twochannels input from the sound pickup section 211-m by a predeterminedfirst coding scheme, furthermore, obtains an extension code includingthe code representing information corresponding to a difference betweenthe input digital sound signals of two channels, and outputs theobtained monaural code and the obtained extension code to the controlinformation granting section 213-m of the sound signal fixedtransmission side unit 210-m. Note that when coding the informationcorresponding to a difference between the input digital sound signals oftwo channels, the coding section 212-m obtains a code by coding theinformation corresponding to a difference between the input digitalsound signals of two channels by a predetermined second coding scheme.

For example, the coding section 212-m obtains a monaural code by codinga sequence of an average value of samples corresponding to the inputdigital sound signals of two channels (i.e., a signal of the M channelof the known MS stereo) by the predetermined first coding scheme, andoutputs the code, furthermore, with samples corresponding to the inputdigital sound signals of two channels, obtains a code by coding asequence (a signal of the S channel of the known MS stereo) of a valueobtained by dividing, by 2, a value obtained by subtracting the sampleof the digital sound signal of the second channel from the sample of thedigital sound signal of the first channel by the predetermined secondcoding scheme, and outputs the obtained code as an extension code.

As the first coding scheme, the same coding scheme is used for thecoding sections 212-m of all sound signal fixed transmission side units210-m and coding sections 312-n of all sound signal mobile transmissionside units 310-n. Thus, as the first coding scheme, it is necessary touse a coding scheme whose bit rate of the monaural code is equal to orsmaller than the communication capacity of the mobile transmission path500-n. In view of this, as the first coding scheme, a coding scheme of aphone band voice for a mobile phone, such as the 13.2 kbps mode of the3GPP EVS standard described above, may be used for example.

The bit rate of the extension code is required to be equal to or smallerthan a value obtained by subtracting the bit rate of the monaural codefrom the communication capacity of the fixed transmission path 400-m.Thus, when coding the information corresponding to a difference betweenthe input digital sound signals of two channels, the same coding scheme,whose bit rate of the extension code is equal to or smaller than a valueobtained by subtracting the bit rate of the monaural code from thecommunication capacity of the fixed transmission path 400-m, is requiredto be used for the coding sections 212-m of all sound signal fixedtransmission side units 210-m as the second coding scheme. As the secondcoding scheme, a coding scheme capable of efficiently coding theinformation corresponding to the difference between the sound signals ofthe two channels, such as a difference signal of the sound signals ofthe two channels, may be used as long as the bit rate of the extensioncode satisfies the above-described condition, for example. Naturally,the same coding scheme as the first coding scheme may be used as thesecond coding scheme, and the 13.2 kbps mode of 3GPP EVS standarddescribed above may be used as the second coding scheme, for example.

Note that the extension code may include a code for obtaining, on thedecoding side, a decoded signal for a quantization error in the codingof a mixed signal of input digital sound signals of two channels by thefirst coding scheme. Specifically, the coding section 212-m may obtain acode representing a quantization error in the coding of a mixed signalof the input digital sound signals of two channels by the first codingscheme, and the obtained code representing a quantization error and theabove-described code representing information corresponding to thedifference may be included in the extension code. Hereafter, a coderepresenting a quantization error is referred to also as an error code,and a code representing information corresponding to a difference isalso referred to as a difference code.

For example, the coding section 212-m obtains a monaural code by codinga sequence of an average value of samples corresponding to the inputdigital sound signals of two channels (i.e., a signal of the M channelof the known MS stereo) by the predetermined first coding scheme, andoutputs the code, obtains a provisional decoded digital sound signalobtained by decoding a monaural code by a first decoding scheme as adecoding method corresponding to the first coding method, and obtains aquantization error sequence by subtracting the sample corresponding tothe provisional decoded digital sound signal from the sample of themixed signal of the input digital sound signals of two channels, then,obtains an error code by coding the obtained quantization errorsequence, and, with the samples corresponding to the input digital soundsignals of two channels, obtains a difference code by coding a sequence(a signal of the S channel of the known MS stereo) of a value obtainedby dividing, by 2, a value obtained by subtracting the sample of thedigital sound signal of the second channel from the sample of thedigital sound signal of the first channel, by the predetermined secondcoding scheme, and outputs an extension code including an error code anda difference code.

Control Information Granting Section 213-m

For each frame, the control information granting section 213-m of thesound signal fixed transmission side unit 210-m obtains a fixed terminalsending bit stream including an input monaural code and an extensioncode as codes representing a sound signal, and a control code that is acode representing code information representing a code included in acode string representing a sound signal and outputs the fixed terminalsending bit stream to the fixed transmission path 400-m (step S213).

The code information represented by the control code included in thefixed terminal sending bit stream output by the control informationgranting section 213-m is always “information representing that a codeincluded in a code string representing a sound signal is a pair of amonaural code and an extension code”. When an input bit stream is afixed terminal sending bit stream, the multipoint control unit 100described later can determine that a code representing a sound signalincluded in the bit stream is a pair of a monaural code and an extensioncode. Thus, when it is intended only for input to the multipoint controlunit 100, it is not necessary to include, in the fixed terminal sendingbit stream, the control code representing code information representinga code included in a code string representing a sound signal, and thesound signal fixed transmission side unit 210-m may not include thecontrol information granting section 213-m, so that the coding section212-m obtains and outputs a fixed terminal sending bit stream includinga monaural code and an extension code as codes representing a soundsignal. Note that the fixed terminal sending bit stream may includeauxiliary information such as information that identifies the terminalapparatus that has obtained the fixed terminal sending bit stream,information that identifies the frame corresponding to the fixedterminal sending bit stream, information that identifies whether theframe includes a sound or not (e.g., whether the power of the digitalsound signal of the frame is not smaller than a predeterminedthreshold), and information that identifies the position of each codeincluded in a fixed terminal sending bit stream in the fixed terminalsending bit stream.

Sound Signal Fixed Reception Side Unit 220-m

For each frame, the sound signal fixed reception side unit 220-m outputsa sound based on a bit stream for a fixed terminal input from the fixedtransmission path 400-m. It should be noted that, depending on the inputbit stream for a fixed terminal, the sound signal fixed reception sideunit 220-m may not output a sound. Note that the bit stream for a fixedterminal input from the fixed transmission path 400-m is a bit streamfor a fixed terminal output by the multipoint control unit 100 to thefixed communication terminal apparatus 200-m.

Control Information Analysis Section 221-m

For each frame, the control information analysis section 221-m of thesound signal fixed reception side unit 220-m outputs, to the decodingsection 222-m of the sound signal fixed reception side unit 220-m, codeinformation represented by the control code included in an input bitstream for a fixed terminal, and each code included in a code stringrepresenting a sound signal included in the input bit stream for a fixedterminal (step S221). It should be noted that the control informationanalysis section 221-m does not output a code when the input bit streamfor a fixed terminal does not include a code string representing a soundsignal. That is, when the input bit stream for a fixed terminal includesa code string representing a sound signal, the control informationanalysis section 221-m outputs, for each frame, code informationrepresented by the control code included in the input bit stream for afixed terminal, and each code included in the code string representing asound signal included in the input bit stream for a fixed terminal andoutputs, when the input bit stream for a fixed terminal does not includea code string representing a sound signal, code information representedby the control code included in the input bit stream for a fixedterminal.

As described later in explanation of the multipoint control unit 100,the pair of code information representing the control code included in abit stream for a fixed terminal and each code included in a code stringrepresenting a sound signal included in the bit stream for a fixedterminal is any of the following case A to case D. Thus, the controlinformation analysis section 221-m outputs at least the code informationof any of the case A to case D. The control information analysis section221-m also outputs a code included in a code string representing a soundsignal when the bit stream for a fixed terminal includes a code stringrepresenting the sound signal.

-   Case A: the code information is “information representing that a    code included in a code string representing a sound signal is a pair    of a monaural code and an extension code”. The code included in the    code string representing a sound signal is a pair of a monaural code    and an extension code.-   Case B: the code information is “information representing that a    code included in a code string representing a sound signal is two    monaural codes”. The code included in the code string representing a    sound signal is two monaural codes.-   Case C: the code information is “information representing that a    code included in a code string representing a sound signal is one    monaural code”. The code included in the code string representing a    sound signal is one monaural code.-   Case D: the code information is “information representing that there    is no code string representing a sound signal”. There is no code    included in the code string representing a sound signal.

Decoding Section 222-m

For each frame, the decoding section 222-m of the sound signal fixedreception side unit 220-m obtains one or two decoded digital soundsignals by decoding the input code, and outputs the one or two signalsto the playback section 223-m of the sound signal fixed reception sideunit 220-m when there is an input code on the basis of the input codeinformation (step S222). More specifically, the decoding section 222-mperforms a process of any of the following case A to case D for eachframe.

Case A

When the input code information is “information representing that a codeincluded in a code string representing a sound signal is a pair of amonaural code and an extension code”, the decoding section 222-m obtainsa provisional decoded digital sound signal by decoding the inputmonaural code by a predetermined first decoding scheme, and obtainsdecoded difference information from a code (difference code)representing information corresponding to a difference included in theinput extension code, from the obtained provisional decoded digitalsound signal and the obtained decoded difference information, obtainsand outputs two decoded digital sound signals by regarding theprovisional decoded digital sound signal as a mixed signal of the twodecoded digital sound signals, and regarding the decoded differenceinformation as information corresponding to a difference between the twodecoded digital sound signals. Note that when the difference code iscoded information, that is, when the difference code is obtained suchthat the information corresponding to a difference between the inputdigital sound signals of two channels is coded by the coding section212-m of the corresponding sound signal fixed transmission side unit210-m by the predetermined second coding scheme, the decoding section222-m obtains decoded difference information by decoding the differencecode included in the input extension code by a predetermined seconddecoding scheme.

For example, the decoding section 222-m obtains a first provisionaldecoded digital sound signal by decoding the input monaural code by thepredetermined first decoding scheme, and obtains a second provisionaldecoded digital sound signal by decoding the difference code included inthe input extension code by the predetermined second decoding scheme,and by taking the first provisional decoded digital sound signal as asignal of the M channel of the known MS stereo, and the secondprovisional decoded digital sound signal as a signal of the S channel ofthe known MS stereo, obtains and outputs a first decoded digital soundsignal, that is a sequence of a value obtained by adding together thecorresponding samples of the first provisional decoded digital soundsignal and the second provisional decoded digital sound signal and asecond decoded digital sound signal, that is a sequence of a valueobtained by subtracting the corresponding sample of the secondprovisional decoded digital sound signal from the corresponding sampleof the first provisional decoded digital sound signal.

Note that when the extension code includes a difference code and anerror code, the decoding section 222-m obtains a provisional decodeddigital sound signal by decoding the input monaural code by thepredetermined first decoding scheme, obtains decoded error informationfrom the error code included in the input extension code, and obtainsdecoded difference information from the difference code included in theinput extension code, then, obtains and outputs two decoded digitalsound signals

from the obtained provisional decoded digital sound signal, the obtaineddecoded error information and the obtained decoded differenceinformation, by regarding the provisional decoded digital sound signalas a mixed signal of the two decoded digital sound signals, regardingthe decoded error information as information corresponding to an errorof the provisional decoded digital sound signal, and regarding thedecoded difference information as information corresponding to adifference between the two decoded digital sound signals.

In this case, for example, the decoding section 222-m obtains the firstprovisional decoded digital sound signal by decoding the input monauralcode by the predetermined first decoding scheme, and obtains a thirdprovisional decoded digital sound signal by decoding an error codeincluded in the input extension code, and obtains the second provisionaldecoded digital sound signal by decoding the difference code included inthe input extension code by the predetermined second decoding scheme,

adds together the first provisional decoded digital sound signal and thethird provisional decoded digital sound signal to obtain a fourthprovisional decoded digital sound signal and, by taking the fourthprovisional decoded digital sound signal as a signal of the M channel ofthe known MS stereo, and taking the second provisional decoded digitalsound signal as a signal of the S channel of the known MS stereo,obtains the first decoded digital sound signal that is a sequence of avalue obtained by adding together corresponding samples of the fourthprovisional decoded digital sound signal and the second provisionaldecoded digital sound signal, and obtains and outputs the second decodeddigital sound signal that is a sequence of a value obtained bysubtracting the corresponding sample of the second provisional decodeddigital sound signal from the corresponding sample of the fourthprovisional decoded digital sound signal.

Case B

When the input code information is “information representing that a codeincluded in a code string representing a sound signal is two monauralcodes, the decoding section 222-m obtains two decoded digital soundsignals by decoding the input two monaural codes by the predeterminedfirst decoding scheme and outputs the signals.

Case C

When the input code information is “information representing that a codeincluded in a code string representing a sound signal is one monauralcode”, the decoding section 222-m obtains one decoded digital soundsignal by decoding the input monaural code by the predetermined firstdecoding scheme and outputs the signal. Note that in this case, asanother decoded digital sound signal, the decoding section 222-m obtainsa decoded digital sound signal corresponding to silence, that is, adecoded digital sound signal in which the amplitudes of all samples are0, and outputs the signal. In addition, in this case, the decodingsection 222-m may obtain, as another decoded digital sound signal, adecoded digital sound signal corresponding to a background noise signalgenerated based on a predetermined rule, such as a decoded digital soundsignal of white noise with a small amplitude and a signal obtained byfiltering the white noise, and output the signal.

Case D

When the information is “information representing that there is no codestring representing a sound signal”, the decoding section 222-m does notperform decoding of codes and does not output a decoded digital soundsignal. Note that in this case, the decoding section 222-m may obtainand output one or two decoded digital sound signals corresponding tosilence, that is, decoded digital sound signals in which the amplitudesof all samples are 0. In addition, in this case, the decoding section222-m may obtain and output one or two decoded digital sound signalscorresponding to a background noise signal generated based on apredetermined rule, such as decoded digital sound signals of white noisewith a small amplitude and signals obtained by filtering the whitenoise.

Note that as the first decoding scheme, the decoding section 222-m usesa decoding scheme corresponding to the first coding scheme used in thecoding section 212-m of the sound signal fixed transmission side unit210-m and the coding section 312-n of the sound signal mobiletransmission side unit 310-n. In addition, as the second decodingscheme, the decoding section 222-m uses a decoding scheme correspondingto the second coding scheme used in the coding section 212-m of thesound signal fixed transmission side unit 210-m.

Playback Section 223-m

The playback section 223-m of the sound signal fixed reception side unit220-m outputs a sound corresponding to one or two input decoded digitalsound signals (step S223). When no decoded digital sound signal isinput, no sound is output.

The playback section 223-m includes two DA conversion sections and twospeakers, for example The DA conversion sections convert an inputdecoded digital sound signal into an analog electric signal and outputsthe signal. The speaker generates a sound corresponding to an analogelectric signal input from the DA conversion sections. The speakers maybe provided in stereo headphones or stereo earphones. In this case, forexample, when two decoded digital sound signals are input, the playbacksection 223-m associates the DA conversion sections with the speakers ina one-to-one relationship, and generates sounds corresponding to the twodecoded digital sound signals from the respective two speakers. Inaddition, when one decoded digital sound signal is input, the playbacksection 223-m obtains one analog electric signal by using one DAconversion section, and generates a sound from one or two speakers byinputting the obtained one analog electric signal to the one or twospeakers. Naturally, even when two decoded digital sound signals areinput, two analog electric signals obtained by the DA conversionsections may be mixed and input to one or two speakers to generate asound from the one or two speakers, or only one speaker may be provided.That is, the playback section 223-m may have any configuration as longas sounds corresponding to all input decoded digital sound signals aregenerated.

Mobile Communication Terminal Apparatus 300-n

Each mobile communication terminal apparatus 300-n is, for example, amobile phone, and includes the sound signal mobile transmission sideunit 310-n and a sound signal mobile reception side unit 320-n asillustrated in FIG. 3. The sound signal mobile transmission side unit310-n includes a sound pickup section 311-n, the coding section 312-nand a sending code generation section 313-n. The sound signal mobilereception side unit 320-n includes an input code separation section321-n, a decoding section 322-n and a playback section 323-n.

The sound signal mobile transmission side unit 310-n of the mobilecommunication terminal apparatus 300-n performs processes of step S311to step S313 exemplified in FIG. 12 and the following description, andthe sound signal mobile reception side unit 320-m of the mobilecommunication terminal apparatus 300-n performs processes of step S321to step S323 exemplified in FIG. 13 and the following description.

Sound Signal Mobile Transmission Side Unit 310-n

For each frame, the sound signal mobile transmission side unit 310-nobtains a mobile terminal sending bit stream that is a bit streamincluding a code corresponding to a digital sound signal of one channel,and outputs the mobile terminal sending bit stream to the mobiletransmission path 500-n. That is, the sound signal mobile transmissionside unit 310-n outputs the mobile terminal sending bit stream to themultipoint control unit 100 through the mobile transmission path 500-n.

Sound Pickup Section 311-n

The sound pickup section 311-n of the sound signal mobile transmissionside unit 310-n includes one microphone and one AD conversion section.The microphone picks up a sound generated in a spatial region of aroundthe microphone, converts the sound into an analog electric signal, andoutputs the analog electric signal to the AD conversion section. The ADconversion section converts an input analog electric signal into adigital sound signal as a PCM signal having a sampling frequency of 8kHz, for example, and outputs the signal. That is, the sound pickupsection 311-n outputs a digital sound signal of one channelcorresponding to a sound picked up by one microphone to the codingsection 312-n of the sound signal mobile transmission side unit 310-n(step S311).

Coding Section 312-n

For each frame, the coding section 312-n of the sound signal mobiletransmission side unit 310-n obtains a monaural code by coding a digitalsound signal of one channel input from the sound pickup section 311-n bythe above-described first coding scheme, and outputs the obtainedmonaural code to the sending code generation section 313-n of the soundsignal mobile transmission side unit 310-n (step S312).

Sending Code Generation Section 313-n

For each frame, the sending code generation section 313-n of the soundsignal mobile transmission side unit 310-n obtains a mobile terminalsending bit stream including the input monaural code as a coderepresenting a sound signal and outputs the mobile terminal sending bitstream to the mobile transmission path 500-n (step S313).

Note that the mobile terminal sending bit stream may include auxiliaryinformation such as information that identifies the terminal apparatusthat has obtained the mobile terminal sending bit stream, informationthat identifies the frame corresponding to the mobile terminal sendingbit stream, information that identifies whether the frame includes asound or not (e.g., whether the power of the digital sound signal of theframe is not smaller than a predetermined threshold), information thatidentifies the position of each code included in the mobile terminalsending bit stream in the mobile terminal sending bit stream, or mayinclude a control code representing code information representing a codeincluded in a code string representing a sound signal. In addition, thesound signal mobile transmission side unit 310-n may not include thesending code generation section 313-n, so that the coding section 312-nobtains and outputs a mobile terminal sending bit stream including amonaural code as a code representing a sound signal.

Sound Signal Mobile Reception Side Unit 320-n

For each frame, the sound signal mobile reception side unit 320-noutputs a sound based on a bit stream for a mobile terminal input fromthe mobile transmission path 500-n. It should be noted that, dependingon the input bit stream for a mobile terminal, the sound signal mobilereception side unit 320-n may not output a sound. Note that the bitstream for a mobile terminal input from the mobile transmission path500-n is a bit stream for a mobile terminal output by the multipointcontrol unit 100 to the mobile communication terminal apparatus 300-n.

Input Code Separation Section 321-n

For each frame, the input code separation section 321-n of the soundsignal mobile reception side unit 320-n outputs, to the decoding section322-n of the sound signal mobile reception side unit 320-n, one monauralcode included in a code string representing a sound signal included inthe input bit stream for a mobile terminal (step S321). It should benoted that, the input code separation section 321-n does not output acode when a code string representing a sound signal is not included inthe input bit stream for a mobile terminal That is, for each frame, theinput code separation section 321-n outputs one monaural code includedin a code string representing a sound signal included in the input bitstream for a mobile terminal when a code string representing a soundsignal is included in the input bit stream for a mobile terminal,whereas the input code separation section 321-n does not output a codewhen a code string representing a sound signal is not included in theinput bit stream for a mobile terminal.

Decoding Section 322-n

For each frame, when a monaural code is input, the decoding section322-n of the sound signal mobile reception side unit 320-n obtains onedecoded digital sound signal by decoding input one monaural code by theabove-described first decoding scheme, and outputs the signal to theplayback section 323-n of the sound signal mobile reception side unit320-n (step S322). When no code is input, the decoding section 322-ndoes not output the decoded digital sound signal. It should be notedthat, when no code is input, the decoding section 322-n may obtain andoutput a decoded digital sound signal corresponding to silence, that is,a decoded digital sound signal in which the amplitudes of all samplesare 0. In addition, when no code is input, the decoding section 322-nmay obtain and output a decoded digital sound signal corresponding to abackground noise signal generated based on a predetermined rule, such asa decoded digital sound signal of white noise with a small amplitude anda signal obtained by filtering the white noise.

Playback Section 323-n

The playback section 323-n of the sound signal mobile reception sideunit 320-n outputs a sound corresponding to one input decoded digitalsound signal (step S323). When no decoded digital sound signal is input,no sound is output.

The playback section 323-n includes one or more DA conversion sectionsand one or more speakers, for example The DA conversion sections convertan input decoded digital sound signal into an analog electric signal andoutputs the signal. The speaker generates a sound corresponding to ananalog electric signal input from the DA conversion sections. Thespeaker may be provided in a headset, headphones or earphones. When aplurality of speakers such as stereo headphones and stereo earphones isused as the speaker, an analog electric signal output by one DAconversion section may be input to the plurality of speakers, or aplurality of analog electric signals obtained by inputting one inputdecoded digital sound signal to a plurality of DA conversion sectionsmay be input to the plurality of speakers. That is, the playback section323-n may have any configuration as long as a sound corresponding to oneinput decoded digital sound signal is generated.

Multipoint Control Unit 100

As illustrated in FIG. 4, the multipoint control unit 100 includes apoint selection section 110 and a bit stream generation section 120. Themultipoint control unit 100 performs the process of step S110 to stepS120 exemplified in FIG. 12 and the following description. A fixedterminal sending bit stream from the fixed transmission path 400-m and amobile terminal sending bit stream from the mobile transmission path500-n are input to the multipoint control unit 100. That is, a fixedterminal sending bit stream output by the sound signal fixedtransmission side unit 210-m of each fixed communication terminalapparatus 200-m is input through each fixed transmission path 400-m, anda mobile terminal sending bit stream output by the sound signal mobiletransmission side unit 310-n of each mobile communication terminalapparatus 300-n is input through each mobile transmission path 500-n.For each frame, the multipoint control unit 100 generates a bit streamfor a fixed terminal for each fixed communication terminal apparatus200-m and outputs the bit stream to each fixed transmission path 400-m,and, the multipoint control unit 100 generates a bit stream for a mobileterminal for each mobile communication terminal apparatus 300-n andoutputs the bit stream to each mobile transmission path 500-n, on thebasis of the input fixed terminal sending bit stream and the inputmobile terminal sending bit stream. Specifically, for each frame, themultipoint control unit 100 generates a bit stream for a fixed terminalfor the sound signal fixed reception side unit 220-m of each fixedcommunication terminal apparatus 200-m and outputs the bit stream to thesound signal fixed reception side unit 220-m of each fixed communicationterminal apparatus 200-m through each fixed transmission path 400-m,generates a bit stream for a mobile terminal for the sound signal mobilereception side unit 320-n of each mobile communication terminalapparatus 300-n and outputs the bit stream to the sound signal mobilereception side unit 320-n of each mobile communication terminalapparatus 300-n through each mobile transmission path 500-n.

Point Selection Section 110

A fixed terminal sending bit stream input to the multipoint control unit100 and a mobile terminal sending bit stream input to the multipointcontrol unit 100 are input to the point selection section 110. For eachframe, the point selection section 110 selects one or two points fromall points connected to the multipoint control unit 100, that is, Mfixed communication terminal apparatuses and N mobile communicationterminal apparatuses, and outputs information that can identify theselected point (step S110). The point selection section 110 may selectthe points based on a selection criterion set in advance, and as theselection criterion, a criterion that can select highly important pointsmay be set in advance so that the point selection section 110 canexecute the selection.

For example, when the power of the sound signal is used as the selectioncriterion, the point selection section 110 obtains, for each frame,information representing the powers of M+N decoded digital sound signalsfrom the monaural codes included in M fixed terminal sending bit streamsand the monaural codes included in N mobile terminal sending bit streamsinput thereto, obtains information that can identify the terminalapparatus corresponding to a decoded digital sound signal having alargest power in the M+N decoded digital sound signals, and informationthat can identify the terminal apparatus corresponding to a decodeddigital sound signal whose power is second largest and is equal to orgreater than a predetermined threshold in the M+N decoded digital soundsignals, and outputs the information to the bit stream generationsection 120 as selection point information. The threshold is, forexample, a value greater than an anticipated power of a decoded digitalsound signal that includes only background noise, and may be set inadvance through an experiment and the like. Thus, the point selectionsection 110 selects one or two points from all points connected to themultipoint control unit 100, and outputs information that can identifythe selected point.

For example, when the terminal apparatus having a decoded digital soundsignal of a largest power is the fixed communication terminal apparatus200-1, the point selection section 110 may obtain information “Fix-1” asthe information that can identify the fixed communication terminalapparatus 200-1. In addition, for example, when the terminal apparatuswhose power of the decoded digital sound signal is second largest and isequal to or greater than a predetermined threshold is the mobilecommunication terminal apparatus 300-2, the point selection section 110may obtain information “Mobile-2” as the information that can identifythe mobile communication terminal apparatus 300-2. Specifically, thepoint selection section 110 outputs information of any of following case1 to case 5 as selection point information.

-   Case 1: “Fix-M₁” (note that M₁ is any one of integers from 1 to M)-   Case 2: “Mobile-N₁” (note that N₁ is any one of integers from 1 to    N)-   Case 3: a pair of “Fix-M₁” and “Fix-M₂” (note that M₁is any one of    integers from 1 to M, and M₂ is any one of integers from 1 to M and    is different from M₁)-   Case 4: a pair of “Fix-M₁” and “Mobile-N₁” (note that M₁ is any one    of integers from 1 to M, and N₁ is any one of integers from 1 to N)-   Case 5: a pair of “Mobile-N₁” and “Mobile-N₂” (note that N₁ is any    one of integers from 1 to N, and N₂ is any one of integers from 1 to    N and is different from N₁)

Note that the information representing the power of each decoded digitalsound signal may be obtained by a known method from each of the input Mfixed terminal sending bit streams and N mobile terminal sending bitstreams. For example, for each frame, the point selection section 110may obtain M+N decoded digital sound signals by decoding the monauralcodes included in the M fixed terminal sending bit streams and themonaural codes included in the N mobile terminal sending bit streamsinput thereto by the above-described first decoding scheme, andcalculate the power of each of the obtained M+N decoded digital soundsignals to obtain the information representing the power. In addition,for example, for each frame, the point selection section 110 may obtain,as the information representing the power, the value represented by eachof the code representing the power included in the monaural codeincluded in the M fixed terminal sending bit streams and the coderepresenting the power included in the monaural code included in the Nmobile terminal sending bit streams.

In addition, when each of the fixed terminal sending bit stream and themobile terminal sending bit stream includes information that identifieswhether the frame includes a sound or not, the point selection section110 may select one or two terminal apparatuses by a known method usingthe input M+N pieces of information that identify whether a sound isincluded or not for each frame, so as to output information that canidentify the selected terminal apparatus as the selection pointinformation to the bit stream generation section 120.

Bit stream Generation Section 120

The fixed terminal sending bit stream input to the multipoint controlunit 100, the mobile terminal sending bit stream input to the multipointcontrol unit 100, and the selection point information output by thepoint selection section 110 are input to the bit stream generationsection 120. For each frame, the bit stream generation section 120 usesthe input fixed terminal sending bit stream and the input mobileterminal sending bit stream on the basis of the input selection pointinformation to generate a bit stream for a fixed terminal to be outputto each fixed communication terminal apparatus 200-m and a bit streamfor a mobile terminal to be output to each mobile communication terminalapparatus 300-n and output the bit streams (step S120). Morespecifically, the bit stream generation section 120 performs any of thefollowing processes for each frame.

Case Where Selection Point Information is Information of Case 1

When the selection point information is information named “Fix-M₁”, thebit stream generation section 120 generates bit streams of threepatterns described below. FIG. 5 schematically illustrates code stringsrepresenting sound signals of this case.

Note that in FIG. 5 and FIGS. 6 to 9 described later, a monaural codeand an extension code included in a fixed terminal sending bit streamoutput by the fixed communication terminal apparatus 200-m are indicatedas CFM_(m) and CFE_(m), respectively, and a monaural code included in amobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-n is indicated as CMM_(n).

The bit stream of the first pattern output by the bit stream generationsection 120 is a bit stream for a fixed terminal that does not include acode string representing a sound signal. If the selection pointinformation is “Fix-M₁”, then the sound required at each terminalapparatus is only the sound picked up by the fixed communicationterminal apparatus 200-M₁. However, because the sound picked up by thefixed communication terminal apparatus 200-M₁ is present in the fixedcommunication terminal apparatus 200-M₁, the multipoint control unit 100is not required to transmit the sound picked up by the fixedcommunication terminal apparatus 200-M₁ to the fixed communicationterminal apparatus 200-M₁. Thus, the bit stream generation section 120generates a bit stream for a fixed terminal that does not include a codestring representing a sound signal and outputs the bit stream to thefixed communication terminal apparatus 200-M₁. More specifically, thebit stream generation section 120 generates a bit stream for a fixedterminal that does not include a code string representing a soundsignal, but includes a control code representing that the codeinformation is “information representing that there is no code stringrepresenting a sound signal”, and outputs the bit stream to a fixedtransmission path 400-M₁ to which the fixed communication terminalapparatus 200-M₁ is connected.

The bit stream of the second pattern output by the bit stream generationsection 120 is a bit stream for a fixed terminal including, as codesrepresenting a sound signal, a monaural code CFM_(M1) and an extensioncode CFE_(M1) included in the fixed terminal sending bit stream outputby the fixed communication terminal apparatus 200-M₁. As describedabove, if the selection point information is “Fix-M₁”, then the soundrequired at each terminal apparatus is only the sound picked up by thefixed communication terminal apparatus 200-M₁. Thus, in each fixedcommunication terminal apparatus 200-m _(else) (m_(else) is an integerfrom 1 to M and is different from M₁) other than the fixed communicationterminal apparatus 200-M₁, it is preferable to output the sound pickedup by the fixed communication terminal apparatus 200-M₁ with the highestpossible quality. Thus, the bit stream generation section 120 generatesa bit stream for a fixed terminal including, as codes representing asound signal, the monaural code CFM_(M1) and the extension code CFE_(M1)included in the fixed terminal sending bit stream output by the fixedcommunication terminal apparatus 200-M₁, and outputs the bit stream toeach fixed communication terminal apparatus 200-m _(else). Morespecifically, the bit stream generation section 120 generates a bitstream for a fixed terminal including the monaural code CFM_(M1) and theextension code CFE_(M1) included in the fixed terminal sending bitstream output by the fixed communication terminal apparatus 200-M₁ ascodes representing a sound signal, and including a control coderepresenting that the code information is “information representing thata code included in a code string representing a sound signal is a pairof a monaural code and an extension code” and outputs the bit stream fora fixed terminal to each fixed transmission path 400-m _(else) to whicheach fixed communication terminal apparatus 200-m _(else) is connected.That is, the code string representing a sound signal included in the bitstream for a fixed terminal for the fixed communication terminalapparatus 200-m _(else) includes the monaural code CFM_(M1) and theextension code CFE_(M1) as codes representing a sound signal.

The bit stream of the third pattern output by the bit stream generationsection 120 is a bit stream for a mobile terminal including, as a coderepresenting a sound signal, the monaural code CFM_(M1) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₁. As described above, if the selection pointinformation is “Fix-M₁”, then the sound required at each terminalapparatus is only the sound picked up by the fixed communicationterminal apparatus 200-M₁. Thus, in each mobile communication terminalapparatus 300-n (n is an integer from 1 to N), it is preferable tooutput the sound picked up by the fixed communication terminal apparatus200-M₁ with the highest possible quality. However, the communicationcapacity of the mobile transmission path 500-n between the multipointcontrol unit 100 and each mobile communication terminal apparatus 300-nis not large enough to send also the extension code in addition to onemonaural code. Thus, the bit stream generation section 120 generates abit stream for a mobile terminal including, as a code representing asound signal, the monaural code CFM_(M1) included in the fixed terminalsending bit stream output by the fixed communication terminal apparatus200-M₁, and outputs the bit stream to each mobile communication terminalapparatus 300-n, that is, to each mobile transmission path 500-n towhich each mobile communication terminal apparatus 300-n is connected.That is, the code string representing a sound signal included in the bitstream for a mobile terminal for the mobile communication terminalapparatus 300-n includes the monaural code CFM_(M1) as a coderepresenting a sound signal.

Case Where Selection Point Information is Information of Case 2

When the selection point information is information named “Mobile-N₁”,the bit stream generation section 120 generates and outputs bit streamsof three patterns described below. FIG. 6 schematically illustrates codestrings representing sound signals of this case.

The bit stream of the first pattern output by the bit stream generationsection 120 is a bit stream for a mobile terminal that does not includea code string representing a sound signal. If the selection pointinformation is “Mobile-N₁”, then the sound required at each terminalapparatus is only the sound picked up by the mobile communicationterminal apparatus 300-N₁. However, because the sound picked up by themobile communication terminal apparatus 300-N₁ is present in the mobilecommunication terminal apparatus 300-N₁, the multipoint control unit 100is not required to transmit the sound picked up by the mobilecommunication terminal apparatus 300-N₁ to the mobile communicationterminal apparatus 300-N₁. Thus, the bit stream generation section 120generates a bit stream for a mobile terminal that does not include acode string representing a sound signal and outputs the bit stream tothe mobile communication terminal apparatus 300-N₁, that is, to themobile transmission path 500-N₁ to which the mobile communicationterminal apparatus 300-N₁ is connected.

The bit stream of the second pattern output by the bit stream generationsection 120 is a bit stream for a mobile terminal including, as a coderepresenting a sound signal, a monaural code CMM_(N1) included in themobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-N₁. As described above, if the selection pointinformation is “Mobile-N₁”, then the sound required at each terminalapparatus is only the sound picked up by the mobile communicationterminal apparatus 300-N₁. Thus, in each mobile communication terminalapparatus 300-n _(else) (n_(else) is an integer from 1 to N and isdifferent from N₁) other than the mobile communication terminalapparatus 300-N₁, it is preferable to output the sound picked up by themobile communication terminal apparatus 300-N₁ with the highest possiblequality. Thus, the bit stream generation section 120 generates a bitstream for a mobile terminal including, as a code representing a soundsignal, the monaural code CMM_(N1) included in the mobile terminalsending bit stream output by the mobile communication terminal apparatus300-N₁, and outputs the bit stream to each mobile communication terminalapparatus 300-n _(else), that is, to each mobile transmission path 500-n_(else) to which each mobile communication terminal apparatus 300-n_(else) is connected. That is, the code string representing a soundsignal included in the bit stream for a mobile terminal for the mobilecommunication terminal apparatus 300-n _(else) includes the monauralcode CMM_(N1) as a code representing a sound signal.

The bit stream of the third pattern output by the bit stream generationsection 120 is a bit stream for a fixed terminal including, as a coderepresenting a sound signal, the monaural code CMM_(N1) included in themobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-N₁. As described above, if the selection pointinformation is “Mobile-N₁”, then the sound required at each terminalapparatus is only the sound picked up by the mobile communicationterminal apparatus 300-N. Thus, in each fixed communication terminalapparatus 200-m (m is an integer from 1 to M), it is preferable tooutput the sound picked up by the mobile communication terminalapparatus 300-N₁ with the highest possible quality. It should be notedthat, the code representing a sound signal included in the mobileterminal sending bit stream output by the mobile communication terminalapparatus 300-N₁ is only the monaural code CMM_(N)i, and no extensioncode is included in the mobile terminal sending bit stream output by themobile communication terminal apparatus 300-N₁. Thus, the bit streamgeneration section 120 generates a bit stream for a fixed terminalincluding, as a code representing a sound signal, the monaural codeCMM_(N1) included in the mobile terminal sending bit stream output bythe mobile communication terminal apparatus 300-N₁, and outputs the bitstream to each fixed communication terminal apparatus 200-m. Morespecifically, the bit stream generation section 120 generates a bitstream for a fixed terminal including the monaural code CMM_(N1)included in the mobile terminal sending bit stream output by the mobilecommunication terminal apparatus 300-N₁as a code representing a soundsignal, and including a control code representing that the codeinformation is “information representing that a code included in a codestring representing a sound signal is one monaural code” and outputs thebit stream to each fixed transmission path 400-m to which each fixedcommunication terminal apparatus 200-m is connected. That is, the codestring representing a sound signal included in the bit stream for afixed terminal for the fixed communication terminal apparatus 200-mincludes the monaural code CMM_(N1) as a code representing a soundsignal.

Case Where Selection Point Information is Information of Case 3

When the selection point information is information named “Fix-M₁” and“Fix-M₂”, the bit stream generation section 120 generates the bit streamof the four patterns described below. It should be noted that, in thecase of M=2, it is not necessary to generate and output the bit streamof the third pattern described below, and therefore the bit streams ofthree patterns of the first, second and fourth patterns described beloware generated and output. FIG. 7 schematically illustrates code stringsrepresenting sound signals of this case.

The bit stream of the first pattern output by the bit stream generationsection 120 is a bit stream for a fixed terminal including, as codesrepresenting a sound signal, the monaural code CFM_(M2) and theextension code CFE_(M2) included in the fixed terminal sending bitstream output by the fixed communication terminal apparatus 200-M₂. Ifthe selection point information is “Fix-M₁” and “Fix-M₂”, then the soundrequired at each terminal apparatus is the sound picked up by the fixedcommunication terminal apparatus 200-M₁ and the sound picked up by thefixed communication terminal apparatus 200-M₂. However, because thesound picked up by the fixed communication terminal apparatus 200-M₁ ispresent in the fixed communication terminal apparatus 200-M₁, themultipoint control unit 100 is not required to transmit the sound pickedup by the fixed communication terminal apparatus 200-M₁ to the fixedcommunication terminal apparatus 200-M₁. Thus, in the fixedcommunication terminal apparatus 200-M₁, it is preferable to output thesound picked up by the fixed communication terminal apparatus 200-M₂with the highest possible quality. Thus, the bit stream generationsection 120 generates a bit stream for a fixed terminal including, ascodes representing a sound signal, the monaural code CFM_(M2) and theextension code CFE_(M2) included in the fixed terminal sending bitstream output by the fixed communication terminal apparatus 200-M₂, andoutputs the bit stream to the fixed communication terminal apparatus200-M₁. More specifically, the bit stream generation section 120generates a bit stream for a fixed terminal including the monaural codeCFM_(M2) and the extension code CFE_(M2) included in the fixed terminalsending bit stream output by the fixed communication terminal apparatus200-M₂ as codes representing a sound signal, and a control coderepresenting that the code information is “information representing thata code included in a code string representing a sound signal is a pairof a monaural code and an extension code”, and outputs the bit stream tothe fixed transmission path 400-M₁ to which the fixed communicationterminal apparatus 200-M₁ is connected. That is, the code stringrepresenting a sound signal included in the bit stream for a fixedterminal for the fixed communication terminal apparatus 200-M₁ includesthe monaural code CFM_(M2) and the extension code CFE_(M2) as codesrepresenting a sound signal.

The bit stream of the second pattern output by the bit stream generationsection 120 is a bit stream for a fixed terminal including, as codesrepresenting a sound signal, a monaural code CFM_(M1) and an extensioncode CFE_(M1) included in the fixed terminal sending bit stream outputby the fixed communication terminal apparatus 200-M₁. As describedabove, if the selection point information is “Fix-M₁” and “Fix-M₂”, thenthe sound required at each terminal apparatus is the sound picked up bythe fixed communication terminal apparatus 200-M₁ and the sound pickedup by the fixed communication terminal apparatus 200-M₂. However,because the sound picked up by the fixed communication terminalapparatus 200-M₂ is present in the fixed communication terminalapparatus 200-M₂, the multipoint control unit 100 is not required totransmit the sound picked up by the fixed communication terminalapparatus 200-M₂ to the fixed communication terminal apparatus 200-M₂.Thus, in the fixed communication terminal apparatus 200-M₂, it ispreferable to output the sound picked up by the fixed communicationterminal apparatus 200-M₁ with the highest possible quality. Thus, thebit stream generation section 120 generates a bit stream for a fixedterminal including, as codes representing a sound signal, the monauralcode CFM_(M1) and the extension code CFE_(M1) included in the fixedterminal sending bit stream output by the fixed communication terminalapparatus 200-M₁, and outputs the bit stream to the fixed communicationterminal apparatus 200-M₂. More specifically, the bit stream generationsection 120 generates a bit stream for a fixed terminal including themonaural code CFM_(M1) and the extension code CFE_(M1) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₁ as codes representing a sound signal andincluding a control code representing that the code information is“information representing that a code included in a code stringrepresenting a sound signal is a pair of a monaural code and anextension code” and outputs the bit stream to the fixed transmissionpath 400-M₂ to which the fixed communication terminal apparatus 200-M₂is connected. That is, the code string representing a sound signalincluded in the bit stream for a fixed terminal for the fixedcommunication terminal apparatus 200-M₂ includes the monaural codeCFM_(M1) and the extension code CFE_(M1) as codes representing a soundsignal.

The bit stream of the third pattern output by the bit stream generationsection 120 is a bit stream for a fixed terminal including, as codesrepresenting a sound signal, the monaural code CFM_(M1) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₁ and the monaural code CFM_(M2) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₂. As described above, if the selection pointinformation is “Fix-M₁” and “Fix-M₂”, then the sound required at eachterminal apparatus is the sound picked up by the fixed communicationterminal apparatus 200-M₁ and the sound picked up by the fixedcommunication terminal apparatus 200-M₂. Thus, in each fixedcommunication terminal apparatus 200-m _(else) (m_(else) is an integerfrom 1 to M and is different from both M₁ and M₂) that is neither thefixed communication terminal apparatus 200-M₁ nor the fixedcommunication terminal apparatus 200-M₂, it is preferable to output thesound picked up by the fixed communication terminal apparatus 200-M₁ andthe sound picked up by the fixed communication terminal apparatus 200-M₂with the highest possible quality. However, the communication capacityof the fixed transmission path 400-m _(else) between the multipointcontrol unit 100 and each fixed communication terminal apparatus 200-m_(else) is not large enough to send also an extension code in additionto two monaural codes. In addition, if the monaural code CFM_(M1) andthe extension code CFE_(M1) included in the fixed terminal sending bitstream output by the fixed communication terminal apparatus 200-M₁ aredecoded to obtain decoded digital sound signals of two channels, and themonaural code CFM_(M2) and the extension code CFE_(M2) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₂ are decoded to obtain decoded digital soundsignals of two channels, and, the two decoded digital sound signals aremixed for each of the two channels and then coded to obtain a monauralcode and an extension code, a pair of a monaural code and an extensioncode can fall within the communication capacity of the fixedtransmission path 400-M_(else) between the multipoint control unit 100and each fixed communication terminal apparatus 200-M_(else), but thesound quality is degraded because paired coding and decoding areconnected in tandem. Thus, the bit stream generation section 120generates a bit stream for a fixed terminal including, as codesrepresenting a sound signal, the monaural code CFM_(M1) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₁ and the monaural code CFM_(M2) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₂, and outputs the bit stream to the fixedcommunication terminal apparatus 200-m _(else). More specifically, thebit stream generation section 120 generates a bit stream for a fixedterminal including the monaural code CFM_(M1) included in the fixedterminal sending bit stream output by the fixed communication terminalapparatus 200-M₁ and the monaural code CFM_(M2) included in the fixedterminal sending bit stream output by the fixed communication terminalapparatus 200-M₂ as codes representing a sound signal, and including acontrol code representing that the code information is “informationrepresenting that a code included in a code string representing a soundsignal is two monaural codes” and outputs the bit stream to each fixedtransmission path 400-m _(else) to which each fixed communicationterminal apparatus 200-m _(else) is connected. That is, the code stringrepresenting a sound signal included in the bit stream for a fixedterminal for the fixed communication terminal apparatus 200-M_(else)includes the monaural code CFM_(M1) and the monaural code CFM_(M2) ascodes representing a sound signal.

The bit stream of the fourth pattern output by the bit stream generationsection 120 is a bit stream for a mobile terminal including, as a coderepresenting a sound signal, a monaural code CTM_(M1M2) obtained bymixing, and then coding, decoded digital sound signals obtained bydecoding each of the monaural code CFM_(M1) included in a fixed terminalsending bit stream output by the fixed communication terminal apparatus200-M₁ and the monaural code CFM_(M2) included in a fixed terminalsending bit stream output by the fixed communication terminal apparatus200-M₂. As described above, if the selection point information is“Fix-M₁” and “Fix-M₂”, then the sound required at each terminalapparatus is the sound picked up by the fixed communication terminalapparatus 200-M₁ and the sound picked up by the fixed communicationterminal apparatus 200-M₂. Thus, in each mobile communication terminalapparatus 300-n (n is an integer from 1 to N), it is preferable tooutput the sound picked up by the fixed communication terminal apparatus200-M₁ and the sound picked up by the fixed communication terminalapparatus 200-M₂ with the highest possible quality. However, thecommunication capacity of the mobile transmission path 500-n between themultipoint control unit 100 and each mobile communication terminalapparatus 300-n is not large enough to send two monaural codes. As such,in each mobile communication terminal apparatus 300-n, it is desirableat least to output the sound picked up by the fixed communicationterminal apparatus 200-M₁ and the sound picked up by the fixedcommunication terminal apparatus 200-M₂, even if the sound quality isdegraded. Thus, the bit stream generation section 120 generates a bitstream for a mobile terminal including, as a code representing a soundsignal, the monaural code CTM_(M1M2) obtained from a mixed digital soundsignal that is obtained at the bit stream generation section 120 byobtaining the first decoded digital sound signal by decoding themonaural code CFM_(M1) included in the fixed terminal sending bit streamoutput by the fixed communication terminal apparatus 200-M₁, byobtaining the second decoded digital sound signal by decoding themonaural code CFM_(M2) included in the fixed terminal sending bit streamoutput by the fixed communication terminal apparatus 200-M₂, byobtaining a mixed digital sound signal by mixing the first decodeddigital sound signal and the second decoded digital sound signal byobtaining a sequence of an average value of the samples corresponding tothe first decoded digital sound signal and the second decoded digitalsound signal or the like, and by obtaining the monaural code CTM_(M1M2)by coding the mixed digital sound signal by the above-described firstcoding scheme and outputs the bit stream to each mobile communicationterminal apparatus 300-n.

That is, the bit stream is output to each mobile transmission path 500-nto which each mobile communication terminal apparatus 300-n isconnected. That is, the code string representing a sound signal includedin the bit stream for a mobile terminal for the mobile communicationterminal apparatus 300-n includes, as a code representing a soundsignal, the monaural code CTM_(M1M2).

Note that when the point selection section 110 has obtained M+N decodeddigital sound signals, the first decoded digital sound signal and thesecond decoded digital signal are the same as two of the M+N decodeddigital sound signals obtained by the point selection section 110, andtherefore, instead of obtaining a decoded digital sound signal bydecoding a monaural code at the bit stream generation section 120, thepoint selection section 110 may output, to the bit stream generationsection 120, the decoded digital sound signal obtained by the pointselection section 110 so that the bit stream generation section 120 usesthe decoded digital sound signal input from the point selection section110.

Case Where Selection Point Information is Information of Case 4

When the selection point information is information named “Fix-M₁” and“Mobile-N₁”, the bit stream generation section 120 generates the bitstream of the four patterns described below. FIG. 8 schematicallyillustrates code strings representing sound signals of this case.

The bit stream of the first pattern output by the bit stream generationsection 120 is a fixed terminal bit stream including, as a coderepresenting a sound signal, the monaural code CMM_(N1) included in themobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-N₁. If the selection point information is“Fix-M₁” and “Mobile-N₁”, then the sound required at each terminalapparatus is the sound picked up by the fixed communication terminalapparatus 200-M₁ and the sound picked up by the mobile communicationterminal apparatus 300-N₁. However, because the sound picked up by thefixed communication terminal apparatus 200-M₁ is present in the fixedcommunication terminal apparatus 200-M₁, the multipoint control unit 100is not required to transmit the sound picked up by the fixedcommunication terminal apparatus 200-M₁ to the fixed communicationterminal apparatus 200-M₁. Thus, in the fixed communication terminalapparatus 200-M₁, it is preferable to output the sound picked up by themobile communication terminal apparatus 300-N₁ with the highest possiblequality. It should be noted that, the code representing a sound signalincluded in the mobile terminal sending bit stream output by the mobilecommunication terminal apparatus 300-N₁ is only the monaural codeCMM_(N1), and no extension code is included in the mobile terminalsending bit stream output by the mobile communication terminal apparatus300-N₁. Thus, the bit stream generation section 120 generates a bitstream for a fixed terminal including, as a code representing a soundsignal, the monaural code CMM_(N1) included in the mobile terminalsending bit stream output by the mobile communication terminal apparatus300-N₁, and outputs the bit stream to the fixed communication terminalapparatus 200-M₁. More specifically, the bit stream generation section120 generates a bit stream for a fixed terminal including the monauralcode CMM_(N1) included in the mobile terminal sending bit stream outputby the mobile communication terminal apparatus 300-N₁ as a coderepresenting a sound signal, and including a control code representingthat the code information is “information representing that a codeincluded in a code string representing a sound signal is one monauralcode” and outputs the bit stream to the fixed transmission path 400-M₁to which the fixed communication terminal apparatus 200-M₁ is connected.That is, the code string representing a sound signal included in the bitstream for a fixed terminal for the fixed communication terminalapparatus 200-M₁ includes the monaural code CMM_(N1) as a coderepresenting a sound signal.

The bit stream of the second pattern output by the bit stream generationsection 120 is a bit stream for a mobile terminal including, as a coderepresenting a sound signal, the monaural code CFM_(M1) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₁. As described above, if the selection pointinformation is “Fix-M₁” and “Mobile-N₁”, then the sound required at eachterminal apparatus is the sound picked up by the fixed communicationterminal apparatus 200-M₁ and the sound picked up by the mobilecommunication terminal apparatus 300-N₁. However, because the soundpicked up by the mobile communication terminal apparatus 300-N₁ ispresent in the mobile communication terminal apparatus 300-N₁, themultipoint control unit 100 is not required to transmit the sound pickedup by the mobile communication terminal apparatus 300-N₁ to the mobilecommunication terminal apparatus 300-N₁. Thus, in the mobilecommunication terminal apparatus 300-N₁, it is preferable to output thesound picked up by the fixed communication terminal apparatus 200-M₁with the highest possible quality. However, the communication capacityof the mobile transmission path 500-N₁ between the multipoint controlunit 100 and the mobile communication terminal apparatus 300-N₁ is notlarge enough to send also the extension code in addition to one monauralcode. Thus, the bit stream generation section 120 generates a bit streamfor a mobile terminal including, as a code representing a sound signal,the monaural code CFM_(M1) included in the fixed terminal sending bitstream output by the fixed communication terminal apparatus 200-M₁, andoutputs the bit stream to the mobile communication terminal apparatus300-N₁, that is, to the mobile transmission path 500-N₁ to which themobile communication terminal apparatus 300-N₁ is connected. That is,the code string representing a sound signal included in the bit streamfor a mobile terminal for the mobile communication terminal apparatus300-N₁ includes the monaural code CFM_(M1) as a code representing asound signal.

The bit stream of the third pattern output by the bit stream generationsection 120 is a bit stream for a fixed terminal including, as codesrepresenting a sound signal, the monaural code CFM_(M1) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₁ and the monaural code CMM_(N1) included in themobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-N₁. As described above, if the selection pointinformation is “Fix-M₁” and “Mobile-N₁”, then the sound required at eachterminal apparatus is the sound picked up by the fixed communicationterminal apparatus 200-M₁ and the sound picked up by the mobilecommunication terminal apparatus 300-N₁. Thus, in each fixedcommunication terminal apparatus 200-m _(else) (m_(else) is an integerfrom 1 to M and is different from M₁) other than the fixed communicationterminal apparatus 200-M₁, it is preferable to output the sound pickedup by the fixed communication terminal apparatus 200-M₁ and the soundpicked up by the mobile communication terminal apparatus 300-N₁ with thehighest possible quality. It should be noted that, the communicationcapacity of the fixed transmission path 400-m _(else) between themultipoint control unit 100 and each fixed communication terminalapparatus 200-m _(else) is not large enough to send also an extensioncode in addition to two monaural codes.

In addition, decoded digital sound signals of two channels are obtainedby decoding the monaural code CFM_(M1) and the extension code CFE_(M1)included in the fixed terminal sending bit stream output by the fixedcommunication terminal apparatus 200-M₁, and a monaural decoded digitalsound signal is obtained by decoding the monaural code CMM_(N1) includedin the mobile terminal sending bit stream output by the mobilecommunication terminal apparatus 300-N₁. Then, after the decoded digitalsound signal and the monaural decoded sound digital sound signal of oneof the two channels are mixed, and the decoded digital sound signal andthe monaural decoded sound digital sound signal of the other channel ofthe two channels are mixed, if coding is performed to obtain a monauralcode and an extension code, a pair of a monaural code and an extensioncode can fall within the communication capacity of the fixedtransmission path 400-m _(else) between the multipoint control unit 100and each fixed communication terminal apparatus 200-m _(else), but thesound quality is degraded because paired coding and decoding areconnected in tandem.

Thus, the bit stream generation section 120 generates a bit stream for afixed terminal including, as codes representing a sound signal, themonaural code CFM_(M1) included in the fixed terminal sending bit streamoutput by the fixed communication terminal apparatus 200-M₁ and themonaural code CMM_(N1) included in the mobile terminal sending bitstream output by the mobile communication terminal apparatus 300-N₁, andoutputs the bit stream to the fixed communication terminal apparatus200-m _(else). More specifically, the bit stream generation section 120generates a bit stream for a fixed terminal including the monaural codeCFM_(M1) included in the fixed terminal sending bit stream output by thefixed communication terminal apparatus 200-M₁ and the monaural codeCMM_(N1) included in the mobile terminal sending bit stream output bythe mobile communication terminal apparatus 300-N₁ as codes representinga sound signal, and including a control code representing that the codeinformation is “information representing that a code included in a codestring representing a sound signal is two monaural codes” and outputsthe bit stream to each fixed transmission path 400-m _(else) to whicheach fixed communication terminal apparatus 200-m _(else) is connected.

That is, the code string representing a sound signal included in the bitstream for a fixed terminal for the fixed communication terminalapparatus 200-m _(else) includes, as codes representing a sound signal,the monaural code CFM_(M1) and the monaural code CMM_(N1).

The bit stream of the fourth pattern output by the bit stream generationsection 120 is a bit stream for a mobile terminal including, as a coderepresenting a sound signal, a monaural code CTM_(M1N1) obtained bymixing, and then coding, a decoded digital sound signals obtained bydecoding each of the monaural code CFM_(M1) included in a fixed terminalsending bit stream output by the fixed communication terminal apparatus200-M₁ and the monaural code CMM_(N1) included in a mobile terminalsending bit stream output by the mobile communication terminal apparatus300-N₁. As described above, if the selection point information is“Fix-M₁” and “Mobile-N₁”, then the sound required at each terminalapparatus is the sound picked up by the fixed communication terminalapparatus 200-M₁ and the sound picked up by the mobile communicationterminal apparatus 300-N₁. Thus, in each mobile communication terminalapparatus 300-n _(else) (n_(else) is an integer from 1 to N and isdifferent from N₁) other than the mobile communication terminalapparatus 300-N₁, it is preferable to output the sound picked up by thefixed communication terminal apparatus 200-M₁ and the sound picked up bythe mobile communication terminal apparatus 300-N₁ with the highestpossible quality. However, the communication capacity of the mobiletransmission path 500-n _(else) between the multipoint control unit 100and each mobile communication terminal apparatus 300-n _(else) is notlarge enough to send two monaural codes. As such, in each mobilecommunication terminal apparatus 300-n _(else), it is desirable at leastto output the sound picked up by the fixed communication terminalapparatus 200-M₁ and the sound picked up by the mobile communicationterminal apparatus 300-N₁ even if the sound quality is degraded.

Thus, the bit stream generation section 120 obtains the first decodeddigital sound signal by decoding the monaural code CFM_(M1) included inthe fixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M_(i), and obtains the second decoded digitalsound signal by decoding the monaural code CMM_(N1) included in themobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-N₁, obtains a mixed digital sound signal bymixing the first decoded digital sound signal and the second decodeddigital sound signal by obtaining a sequence of an average value of thesamples corresponding to the first decoded digital sound signal and thesecond decoded digital sound signal or the like, obtains the monauralcode CTM_(M1N1) by coding the mixed digital sound signal by theabove-described first coding scheme, generates a bit stream for a mobileterminal including the monaural code CTM_(M1N1) obtained from the mixeddigital sound signal as a code representing the sound signal and outputsthe bit stream for a mobile terminal to the mobile communicationterminal apparatus 300-n _(else), that is, to each mobile transmissionpath 500-n _(else) to which each communication terminal apparatus 300-n_(else) is connected. That is, the code string representing a soundsignal included in the bit stream for a mobile terminal for the mobilecommunication terminal apparatus 300-n _(else) includes, as a coderepresenting a sound signal, the monaural code CTM_(M1N1).

Note that when the point selection section 110 has obtained M+N decodeddigital sound signals, the first decoded digital sound signal and thesecond decoded digital signal are the same as two of the M+N decodeddigital sound signals obtained by the point selection section 110, andtherefore, instead of obtaining a decoded digital sound signal bydecoding a monaural code at the bit stream generation section 120, thepoint selection section 110 may output, to the bit stream generationsection 120, the decoded digital sound signal obtained by the pointselection section 110 so that the bit stream generation section 120 usesthe decoded digital sound signal input from the point selection section110.

Case Where Selection Point Information is Information of Case 5

When the selection point information is information named “Mobile-N₁”and “Mobile-N₂”, the bit stream generation section 120 generates the bitstream of any of the four patterns described below. It should be notedthat, in the case of N=2, it is not necessary to generate and output thebit stream of the third pattern described below, and therefore bitstreams of three patterns of the first, second and fourth patternsdescribed below are generated. FIG. 9 schematically illustrates codestrings representing sound signals of this case.

The bit stream of the first pattern output by the bit stream generationsection 120 is a bit stream for a mobile terminal including, as a coderepresenting a sound signal, a monaural code CMM_(N2) included in themobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-N₂. If the selection point information is“Mobile-N₁” and “Mobile-N₂”, then the sound required at each terminalapparatus is the sound picked up by the mobile communication terminalapparatus 300-N₁ and the sound picked up by the mobile communicationterminal apparatus 300-N₂. However, because the sound picked up by themobile communication terminal apparatus 300-N₁ is present in the mobilecommunication terminal apparatus 300-N₁, the multipoint control unit 100is not required to transmit the sound picked up by the mobilecommunication terminal apparatus 300-N₁ to the mobile communicationterminal apparatus 300-N₁. Thus, in the mobile communication terminalapparatus 300-N₁, it is preferable to output the sound picked up by themobile communication terminal apparatus 300-N₂ with the highest possiblequality. Thus, the bit stream generation section 120 generates a bitstream for a mobile terminal including, as a code representing a soundsignal, the monaural code CMM_(N2) included in the mobile terminalsending bit stream output by the mobile communication terminal apparatus300-N₂, and outputs the bit stream to the mobile communication terminalapparatus 300-N₁, that is, to the mobile transmission path 500-N₁ towhich the mobile communication terminal apparatus 300-N₁ is connected.That is, the code string representing a sound signal included in the bitstream for a mobile terminal for the mobile communication terminalapparatus 300-N₁ includes, as a code representing a sound signal, themonaural code CMM_(N2).

The bit stream of the second pattern output by the bit stream generationsection 120 is a bit stream for a mobile terminal including, as a coderepresenting a sound signal, a monaural code CMM_(N1) included in themobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-N₁. As described above, if the selection pointinformation is “Mobile-N₁” and “Mobile-N₂”, then the sound required ateach terminal apparatus is the sound picked up by the mobilecommunication terminal apparatus 300-N₁ and the sound picked up by themobile communication terminal apparatus 300-N₂. However, because thesound picked up by the mobile communication terminal apparatus 300-N₂ ispresent in the mobile communication terminal apparatus 300-N₂, themultipoint control unit 100 is not required to transmit the sound pickedup by the mobile communication terminal apparatus 300-N₂ to the mobilecommunication terminal apparatus 300-N₂. Thus, in the mobilecommunication terminal apparatus 300-N₂, it is preferable to output thesound picked up by the mobile communication terminal apparatus 300-N₁with the highest possible quality. Thus, the bit stream generationsection 120 generates a bit stream for a mobile terminal including, as acode representing a sound signal, the monaural code CMM_(N1) included inthe mobile terminal sending bit stream output by the mobilecommunication terminal apparatus 300-N₁, and outputs the bit stream tothe mobile communication terminal apparatus 300-N₂, that is, to a mobiletransmission path 500-N₂ to which the mobile communication terminalapparatus 300-N₂ is connected. That is, the code string representing asound signal included in the bit stream for a mobile terminal for themobile communication terminal apparatus 300-N₂ includes the monauralcode CMM_(N1) as a code representing a sound signal.

The bit stream of the third pattern output by the bit stream generationsection 120 is a bit stream for a mobile terminal including, as a coderepresenting a sound signal, a monaural code CTM_(N1N2) obtained bymixing, and then coding, a decoded digital sound signals obtained bydecoding each of the monaural code CMM_(N1) included in a mobileterminal sending bit stream output by the mobile communication terminalapparatus 300-N₁ and the monaural code CMM_(N2) included in a mobileterminal sending bit stream output by the mobile communication terminalapparatus 300-N₂. As described above, if the selection point informationis “Mobile-N₁” and “Mobile-N₂”, then the sound required at each terminalapparatus is the sound picked up by the mobile communication terminalapparatus 300-N₁ and the sound picked up by the mobile communicationterminal apparatus 300-N₂. Thus, in each mobile communication terminalapparatus 300-n _(else) (n_(else) is an integer from 1 to N and isdifferent from both N₁ and N₂) that is neither the mobile communicationterminal apparatus 300-N₁ nor the mobile communication terminalapparatus 300-N₂, it is preferable to output the sound picked up by themobile communication terminal apparatus 300-N₁ and the sound picked upby the mobile communication terminal apparatus 300-N₂ with the highestpossible quality. However, the communication capacity of the mobiletransmission path 500-n _(else) between the multipoint control unit 100and each mobile communication terminal apparatus 300-n _(else) is notlarge enough to send two monaural codes. As such, in each mobilecommunication terminal apparatus 300-n _(else), it is desirable at leastto output the sound picked up by the mobile communication terminalapparatus 300-N₁ and the sound picked up by the mobile communicationterminal apparatus 300-N₂ even if the sound quality is degraded.

Thus the bit stream generation section 120 obtains the first decodeddigital sound signal by decoding the monaural code CMM_(N1) included inthe mobile terminal sending bit stream output by the mobilecommunication terminal apparatus 300-N₁, and obtains the second decodeddigital sound signal by decoding the monaural code CMM_(N2) included inthe mobile terminal sending bit stream output by the mobilecommunication terminal apparatus 300-N₂, obtains a mixed digital soundsignal by mixing the first decoded digital sound signal and the seconddecoded digital sound signal by obtaining a sequence of an average valueof the samples corresponding to the first decoded digital sound signaland the second decoded digital sound signal, and the like, further,obtains the monaural code CTM_(N1N2) by coding the mixed digital soundsignal by the above-described first coding scheme, generates a bitstream for a mobile terminal including, as a code representing a soundsignal, the monaural code CTM_(N1N2) obtained from a mixed digital soundsignal, and outputs the bit stream to each mobile communication terminalapparatus 300-n _(else), that is, to each mobile transmission path 500-n_(else) to which each mobile communication terminal apparatus 300-n_(else) is connected. That is, the code string representing a soundsignal included in the bit stream for a mobile terminal for the mobilecommunication terminal apparatus 300-n _(else) includes, as a coderepresenting a sound signal, the monaural code CTM_(N1N2).

Note that when the point selection section 110 has obtained M+N decodeddigital sound signals, the first decoded digital sound signal and thesecond decoded digital signal are the same as two of the M+N decodeddigital sound signals obtained by the point selection section 110, andtherefore, instead of obtaining a decoded digital sound signal bydecoding a monaural code at the bit stream generation section 120, thepoint selection section 110 may output, to the bit stream generationsection 120, the decoded digital sound signal obtained by the pointselection section 110 so that the bit stream generation section 120 usesthe decoded digital sound signal input from the point selection section110.

The bit stream of the fourth pattern output by the bit stream generationsection 120 is a bit stream for a fixed terminal including, as codesrepresenting a sound signal, the monaural code CMM_(N1) included in themobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-N₁ and the monaural code CMM_(N2) included in themobile terminal sending bit stream output by the mobile communicationterminal apparatus 300-N₂. As described above, if the selection pointinformation is “Mobile-N₁” and “Mobile-N₂”, then the sound required ateach terminal apparatus is the sound picked up by the mobilecommunication terminal apparatus 300-N₁ and the sound picked up by themobile communication terminal apparatus 300-N₂. Thus, in each fixedcommunication terminal apparatus 200-m (m is an integer from 1 to M), itis preferable to output the sound picked up by the mobile communicationterminal apparatus 300-N₁ and the sound picked up by the mobilecommunication terminal apparatus 300-N₁ with the highest possiblequality. Thus, the bit stream generation section 120 generates a bitstream for a fixed terminal including, as codes representing a soundsignal, the monaural code CMM_(N)i included in the mobile terminalsending bit stream output by the mobile communication terminal apparatus300-N₁ and the monaural code CMM_(N2) included in the mobile terminalsending bit stream output by the mobile communication terminal apparatus300-N₂, and outputs the bit stream to the fixed communication terminalapparatus 200-m. More specifically, the bit stream generation section120 generates a bit stream for a fixed terminal including the monauralcode CMM_(N1) included in the fixed terminal sending bit stream outputby the mobile communication terminal apparatus 300-N₁ and the monauralcode CMM_(N2) included in the mobile terminal sending bit stream outputby the mobile communication terminal apparatus 300-N₂ as codesrepresenting a sound signal, and including a control code representingthat the code information is “information representing that a codeincluded in a code string representing a sound signal is two monauralcodes” and outputs the bit stream to each fixed transmission path 400-mto which each fixed communication terminal apparatus 200-m is connected.That is, the code string representing a sound signal included in the bitstream for a fixed terminal for the fixed communication terminalapparatus 200-m includes, as codes representing a sound signal, themonaural code CMM_(N1) and the monaural code CMM_(N2).

Operation of Multipoint Phone Connection System 10

Next, a frame-wise operation of the multipoint phone connection system10 according to the first embodiment, that is, a multipoint phoneconnection method performed by the multipoint phone connection system 10according to the first embodiment for each frame is described.

Up to the point where a bit stream is transmitted to the multipointcontrol unit 100 from each terminal apparatus, the multipoint phoneconnection system 10 performs the same operation in any of the casesdescribed below. More specifically, in any of the cases described below,each fixed communication terminal apparatus 200-m obtains a monauralcode CFM_(m) by coding a mixed signal of picked-up digital sound signalsof two channels by the first coding scheme, obtains a code representinginformation corresponding to a difference between the picked-up digitalsound signals of two channels as an extension code CFE_(m), and outputsthe obtained monaural code CFM_(m) and the obtained extension codeCI-B_(m) to the multipoint control unit 100 as codes representing thepicked-up digital sound signals of two channels. In addition, in any ofthe cases described below, each mobile communication terminal apparatus300-n obtains a monaural code CMM_(m) by coding a picked-up digitalsound signal of one channel by the first coding scheme, and outputs theobtained monaural code CMM_(m) as a code representing the picked-updigital sound signal of one channel to the multipoint control unit 100.

After the bit stream is transmitted to the multipoint control unit 100from each terminal apparatus, the multipoint phone connection system 10performs the following operation for each case described below.

Case Where Only Fixed Communication Terminal Apparatus 200-M₁ (M₁ is anyone of integers from 1 to M) is Selected

In the above-described example in which the power of the sound signal isused as the selection criterion, this case corresponds to a case wherethe fixed communication terminal apparatus 200-M₁ has a sound signal ofa largest power in M+N terminal apparatuses, and the power of the soundsignal whose power is second largest is smaller than a threshold.

In this case, the point selection section 110 of the multipoint controlunit 100 outputs the selection point information of the above-describedcase 1, and the bit stream generation section 120 of the multipointcontrol unit 100 performs the operation of the above-described “CaseWhere Selection Point Information is Information of Case 1”, andtherefore, the multipoint phone connection system 10 operates in thefollowing manner, which includes subsequent operations of each terminalapparatus.

-   -   The multipoint control unit 100 does not output a code        representing a sound signal to the fixed communication terminal        apparatus 200-M₁. The fixed communication terminal apparatus        200-M₁ does not decode a code representing a sound signal and        does not obtain a decoded sound signal.    -   The multipoint control unit 100 outputs, to each fixed        communication terminal apparatus 200-m _(else) (m_(else) is an        integer from 1 to M and is different from M₁) other than the        fixed communication terminal apparatus 200-M₁, the extension        code CFE_(M1) and the monaural code CFM_(M1) representing the        sound signal of the two-channel stereo picked up by the fixed        communication terminal apparatus 200-M₁. From the monaural code        CFM_(M1) and the extension code CFE_(M1) output by the        multipoint control unit 100, each fixed communication terminal        apparatus 200-m _(else) obtains a decoded sound signal of        two-channel stereo corresponding to the sound signal of the        two-channel stereo picked up by the fixed communication terminal        apparatus 200-M₁ by performing the process of the        above-described case A.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n (n is an integer from 1        to N), only the monaural code CFM_(M1) of the codes representing        a sound signal of the two-channel stereo picked up by the fixed        communication terminal apparatus 200-M₁. From the monaural code        CFM_(M1) output by the multipoint control unit 100, each mobile        communication terminal apparatus 300-n obtains a monaural        decoded sound signal in which a sound signal of the two-channel        stereo picked up by the fixed communication terminal apparatus        200-M₁.

Note that in an example of a voice conference, this case corresponds toa frame in which only the fixed communication terminal apparatus 200-M₁is the voice source point, and the multipoint phone connection system 10operates as follows.

-   -   The multipoint control unit 100 does not output a code        representing a sound signal to the fixed communication terminal        apparatus 200-M₁ of the voice source point. The fixed        communication terminal apparatus 200-M₁ does not decode a code        representing a sound signal and does not obtain a decoded sound        signal.    -   The multipoint control unit 100 outputs, to each fixed        communication terminal apparatus 200-M_(else) that is not the        voice source point, the monaural code CFM_(M1) and the extension        code CFE_(M1) representing the sound signal of the two-channel        stereo of the voice source point. From the monaural code        CFM_(M1) and the extension code CFE_(M1) output by the        multipoint control unit 100, each fixed communication terminal        apparatus 200-m _(else) that is not the voice source point        obtains, by performing the process of the above-described case        A, a decoded sound signal of two-channel stereo that is a sound        signal corresponding to the sound signal of the two-channel        stereo of the voice source point, in which paired coding and        decoding are not connected in tandem.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n, only the monaural code        CFM_(M1) of codes representing a sound signal of two-channel        stereo of the voice source point. From the monaural code        CFM_(M1) output by the multipoint control unit 100, each mobile        communication terminal apparatus 300-n obtains a monaural        decoded sound signal that is a mixed sound signal of the sound        signal of the two-channel stereo of the voice source point in        which paired coding and decoding are not connected in tandem.        Case Where Only Mobile Communication Terminal Apparatus 300-N₁        (N₁ is any one of integers from 1 to N) is Selected

In the above-described example in which the power of the sound signal isused as the selection criterion, this case corresponds to a case wherethe mobile communication terminal apparatus 300-N₁ has a sound signal ofa largest power in M+N terminal apparatuses, and the power of the soundsignal whose power is second largest is smaller than a threshold.

In this case, the point selection section 110 of the multipoint controlunit 100 outputs the selection point information of the above-describedcase 2, and the bit stream generation section 120 of the multipointcontrol unit 100 performs the operation of the above-described “CaseWhere Selection Point Information is Information of Case 2”, andtherefore, the multipoint phone connection system 10 operates in thefollowing manner, which includes subsequent operations of each terminalapparatus.

-   -   The multipoint control unit 100 does not output a code        representing a sound signal to the mobile communication terminal        apparatus 300-N₁. The mobile communication terminal apparatus        300-N₁ does not decode a code representing a sound signal and        does not obtain a decoded sound signal.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n _(else) (n_(else) is an        integer from 1 to N and is different from N₁) other than the        mobile communication terminal apparatus 300-N₁, the monaural        code CMM_(N1) representing a monaural sound signal picked up by        the mobile communication terminal apparatus 300-N₁. From the        monaural code CMM_(N1) output by the multipoint control unit        100, each mobile communication terminal apparatus 300-n _(else)        obtains a monaural decoded sound signal corresponding to the        monaural sound signal picked up by the mobile communication        terminal apparatus 300-N₁.    -   The multipoint control unit 100 outputs, to each fixed        communication terminal apparatus 200-m (m is an integer from 1        to M), the monaural code CMM_(N1) representing the monaural        sound signal picked up by the mobile communication terminal        apparatus 300-N₁. From the monaural code CMM_(N1) output by the        multipoint control unit 100, each fixed communication terminal        apparatus 200-m obtains, by performing the process of the        above-described case C, a monaural decoded sound signal        corresponding to the monaural sound signal picked up by the        mobile communication terminal apparatus 300-N₁.

Note that in an example of a voice conference, this case corresponds toa frame in which only the mobile communication terminal apparatus 300-N₁is the voice source point, and the multipoint phone connection system 10operates as follows.

-   -   The multipoint control unit 100 does not output a code        representing a sound signal to the mobile communication terminal        apparatus 300-N₁ of the voice source point. The mobile        communication terminal apparatus 300-N₁ does not decode a code        representing a sound signal and does not obtain a decoded sound        signal.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n _(else) that is not the        voice source point, the monaural code CMM_(N1) representing the        monaural sound signal of the voice source point. From the        monaural code CMM_(N1) output by the multipoint control unit        100, each mobile communication terminal apparatus 300-n _(else)        that is not the voice source point obtains a monaural decoded        sound signal that is a sound signal corresponding to the        monaural sound signal of the voice source point in which paired        coding and decoding are not connected in tandem.    -   The multipoint control unit 100 outputs, to each fixed        communication terminal apparatus 200-m, the monaural code        CMM_(N1) representing the monaural sound signal of the voice        source point. From the monaural code CMM_(N1) output by the        multipoint control unit 100, each fixed communication terminal        apparatus 200-m obtains, by performing the process of the        above-described case C, a monaural decoded sound signal that is        a sound signal corresponding to the monaural sound signal of the        voice source point in which paired coding and decoding are not        connected in tandem.        Case Where Fixed Communication Terminal Apparatus 200-M₁ (M₁ is        any one of integers from 1 to M) and Fixed Communication        Terminal Apparatus 200-M₂ (M₂ is any one of integers from 1 to M        and is different from M₁) are Selected

In the above-described example in which the power of the sound signal isused as the selection criterion, this case corresponds to a case wherean apparatus whose power of the sound signal is largest and an apparatuswhose power is second largest and is equal to or greater than athreshold in M+N terminal apparatuses are the fixed communicationterminal apparatus 200-M₁ and the fixed communication terminal apparatus200-M₂.

In this case, the point selection section 110 of the multipoint controlunit 100 outputs the selection point information of the above-describedcase 3, and the bit stream generation section 120 of the multipointcontrol unit 100 performs the operation of the above-described “CaseWhere Selection Point Information is Information of Case 3”, andtherefore, the multipoint phone connection system 10 operates in thefollowing manner, which includes subsequent operations of each terminalapparatus.

-   -   The multipoint control unit 100 outputs, to the fixed        communication terminal apparatus 200-M₁, the monaural code        CFM_(M2) and the extension code CFE_(M2) representing the sound        signal of the two-channel stereo picked up by the fixed        communication terminal apparatus 200-M₂. From the monaural code        CFM_(M2) and the extension code CFE_(M2) output by the        multipoint control unit 100, the fixed communication terminal        apparatus 200-M₁ obtains, by performing the process of the        above-described case A, a decoded sound signal of two-channel        stereo corresponding to the sound signal of the two-channel        stereo picked up by the fixed communication terminal apparatus        200-M₂.    -   The multipoint control unit 100 outputs, to the fixed        communication terminal apparatus 200-M₂, the extension code        CFE_(M1) and the monaural code CFM_(M1) representing the sound        signal of the two-channel stereo picked up by the fixed        communication terminal apparatus 200-M₁. From the monaural code        CFM_(M1) and the extension code CFE_(M1) output by the        multipoint control unit 100, the fixed communication terminal        apparatus 200-M₂ obtains, by performing the process of the        above-described case A, a decoded sound signal of two-channel        stereo corresponding to the sound signal of the two-channel        stereo picked up by the fixed communication terminal apparatus        200-M₁.    -   The multipoint control unit 100 outputs, to each fixed        communication terminal apparatus 200-M_(else) (m_(else) is an        integer from 1 to M and is different from both M₁ and M₂) that        is neither the fixed communication terminal apparatus 200-M₁ nor        the fixed communication terminal apparatus 200-M₂, the monaural        code CFM_(M1) of the codes representing a sound signal of the        two-channel stereo picked up by the fixed communication terminal        apparatus 200-M₁, and the monaural code CFM_(M2) of the codes        representing a sound signal of two-channel stereo picked up by        the fixed communication terminal apparatus 200-M₂. From the two        monaural codes CFM_(M1) and CFM_(M2) output by the multipoint        control unit 100, each fixed communication terminal apparatus        200-m _(else) obtains, by performing the process of the        above-described case B, decoded sound signals of two channels,        namely, a monaural decoded sound signal in which the sound        signal of the two-channel stereo picked up by the fixed        communication terminal apparatus 200-M₁ is mixed, and a monaural        decoded sound signal in which the sound signal of the        two-channel stereo picked up by the fixed communication terminal        apparatus 200-M₂ is mixed.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n (n is an integer from 1        to N), the monaural code CTM_(M1M2) obtained by mixing, and then        coding a sound signal obtained by decoding the monaural code        CFM_(M1) of the codes representing a sound signal of the        two-channel stereo picked up by the fixed communication terminal        apparatus 200-M₁ and a sound signal obtained by decoding the        monaural code CFM_(M1) of the codes representing a sound signal        of two-channel stereo picked up by the fixed communication        terminal apparatus 200-M₂. From one monaural code CTM_(M1M2)        output by the multipoint control unit 100, each mobile        communication terminal apparatus 300-n obtains one monaural        decoded sound signal corresponding to a mixed sound signal of        the sound signal of the two-channel stereo picked up by the        fixed communication terminal apparatus 200-M₁ and the sound        signal of the two-channel stereo picked up by the fixed        communication terminal apparatus 200-M₂.

Note that in an example of a voice conference, this case corresponds toa frame in which the two points, the fixed communication terminalapparatus 200-M₁ and the fixed communication terminal apparatus 200-M₂,are the voice source points, and the multipoint phone connection system10 operates as follows.

-   -   The multipoint control unit 100 outputs, to the fixed        communication terminal apparatus 200-M₁ and the fixed        communication terminal apparatus 200-M₂ of the voice source        points, an extension code CFE_(Mx) and a monaural code CFM_(Mx)        (x is 1 or 2) representing the sound signal of the two-channel        stereo of the other voice source point. From the monaural code        CFM_(MX) and the extension code CFE_(Mx) output by the        multipoint control unit 100, each of the fixed communication        terminal apparatus 200-M₁ and the fixed communication terminal        apparatus 200-M₂ of the voice source points obtains, by        performing the process of the above-described case A, a decoded        sound signal of two-channel stereo that is a sound signal        corresponding to the sound signal of the two-channel stereo of        the other voice source point in which paired coding and decoding        are not connected in tandem.    -   The multipoint control unit 100 outputs, to each fixed        communication terminal apparatus 200-m _(else) that is not the        voice source point, the monaural codes CFM_(M1) and CFM_(M2) of        codes representing sound signals of two-channel stereo of the        two voice source points. From the two monaural codes CFM_(M1)        and CFM_(M2) output by the multipoint control unit 100, each        fixed communication terminal apparatus 200-m _(else) that is not        the voice source point obtains, by performing the process of the        above-described case B, decoded sound signals of two channels        that are two monaural sound signals corresponding to sound        signals, each of which is a mixed sound signal of the        two-channel stereo of each voice source point and in which        paired coding and decoding are not connected in tandem.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n, the monaural code        CTM_(M1M2) representing one sound signal obtained by mixing, and        then coding, two sound signals obtained by decoding the monaural        codes CFM_(M1) and CFM_(M2) of the codes representing sound        signals of two-channel stereo of the two voice source points.        From one monaural code CTM_(M1M2) output by the multipoint        control unit 100, each mobile communication terminal apparatus        300-n obtains one decoded sound signal that is a mixed monaural        sound signal of all sound signals of the two voice source points        in which paired coding and decoding are connected in tandem.        Case Where Fixed Communication Terminal Apparatus 200-M₁ (M₁ is        any one of integers from 1 to M) and the Mobile Communication        Terminal Apparatus 300-N₁ (N₁ is any one of integers from 1        to N) are Selected

In the above-described example in which the power of the sound signal isused as the selection criterion, this case corresponds to a case wherean apparatus whose power of the sound signal is largest and an apparatuswhose power is second largest and is equal to or greater than athreshold in M+N terminal apparatuses are the fixed communicationterminal apparatus 200-M₁ and the mobile communication terminalapparatus 300-N₁.

In this case, the point selection section 110 of the multipoint controlunit 100 outputs the selection point

information of the above-described case 4, and the bit stream generationsection 120 of the multipoint control unit 100 performs the operation ofthe above-described “Case Where Selection Point Information isInformation of Case 4”, and therefore, the multipoint phone connectionsystem 10 operates in the following manner, which includes subsequentoperations of each terminal apparatus.

-   -   The multipoint control unit 100 outputs, to the fixed        communication terminal apparatus 200-M₁, the monaural code        CMM_(N1) representing a monaural sound signal picked up by the        mobile communication terminal apparatus 300-N₁. From one        monaural code CMM_(N1) output by the multipoint control unit        100, the fixed communication terminal apparatus 200-M₁obtains,        by performing the process of the above-described case C, a        monaural decoded sound signal corresponding to the monaural        sound signal picked up by the mobile communication terminal        apparatus 300-N₁.    -   The multipoint control unit 100 outputs, to the mobile        communication terminal apparatus 300-N₁, a monaural code        CFM_(M1) of the codes representing a sound signal of the        two-channel stereo picked up by the fixed communication terminal        apparatus 200-M₁. From one monaural code CFM_(M1) output by the        multipoint control unit 100, the mobile communication terminal        apparatus 300-N₁ obtains a monaural decoded sound signal in        which the sound signal of the two-channel stereo picked up by        the fixed communication terminal apparatus 200-M₁ is mixed.    -   The multipoint control unit 100 outputs, to each fixed        communication terminal apparatus 200-M_(else) (M_(else) is an        integer from 1 to M and is different from M₁) that is not the        fixed communication terminal apparatus 200-M₁, the monaural code        CFM_(M1) of the codes representing a sound signal of the        two-channel stereo picked up by the fixed communication terminal        apparatus 200-M₁ and the monaural code CMM_(N1) representing a        monaural sound signal picked up by the mobile communication        terminal apparatus 300-N₁. From the two monaural codes CFM_(M1)        and CMM_(N1) output by the multipoint control unit 100, each        fixed communication terminal apparatus 200-m _(else) obtains, by        performing the process of the above-described case B, decoded        sound signals of two channels, namely, a monaural sound signal        in which the sound signal of the two-channel stereo picked up by        the fixed communication terminal apparatus 200-M₁ is mixed, and        a monaural sound signal corresponding to the monaural sound        signal picked up by the mobile communication terminal apparatus        300-N₁.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n _(else) (n_(else) is an        integer from 1 to N and is different from N₁) that is not the        mobile communication terminal apparatus 300-N₁, the monaural        code CTM_(M1N1) obtained by mixing, and then coding a sound        signal obtained by decoding the monaural code CFM_(M1) of the        codes representing a sound signal of the two-channel stereo        picked up by the fixed communication terminal apparatus 200-M₁        and a sound signal obtained by decoding the monaural code        CMM_(N1) representing a monaural sound signal picked up by the        mobile communication terminal apparatus 300-N₁. From one        monaural code CTM_(M1N1) output from the multipoint control unit        100, each mobile communication terminal apparatus 300-n _(else)        obtains one monaural decoded sound signal corresponding to a        mixed sound signal of the sound signal of the two-channel stereo        picked up by the fixed communication terminal apparatus 200-M₁        and the monaural sound signal picked up by the mobile        communication terminal apparatus 300-N₁.

Note that in an example of a voice conference, this case corresponds toa frame in which the two points, the fixed communication terminalapparatus 200-M₁ and the mobile communication terminal apparatus 300-N₁,are voice source points, and the multipoint phone connection system 10operates as follows.

-   -   The multipoint control unit 100 outputs, to the fixed        communication terminal apparatus 200-M₁ of the voice source        point, the monaural code CMM_(N1) representing the sound signal        of the other voice source point. From one monaural code CMM_(N1)        output by the multipoint control unit 100, the fixed        communication terminal apparatus 200-M₁ of the voice source        point obtains, by performing the process of the above-described        case C, a monaural decoded sound signal that is a monaural sound        signal corresponding to the monaural sound signal of the other        voice source point in which paired coding and decoding are not        connected in tandem.    -   The multipoint control unit 100 outputs, to the mobile        communication terminal apparatus 300-N₁ of the voice source        point, only the monaural code CFM_(M1) of codes representing a        sound signal of two-channel stereo of the other voice source        point. From one monaural code CFM_(M1) output by the multipoint        control unit 100, the mobile communication terminal apparatus        300-N₁ obtains a monaural decoded sound signal that is a mixed        sound signal of the sound signal of the two-channel stereo of        the other voice source point in which paired coding and decoding        are not connected in tandem. p1 The multipoint control unit 100        outputs, to each fixed communication terminal apparatus        200-M_(else) that is not the voice source point, the two        monaural codes CFM_(M1) and CMM_(N1) representing the sound        signals of the two voice source points. That is, the monaural        code CFM_(M1) of the codes representing the sound signal of the        two-channel stereo of one voice source point and the monaural        code CMM_(N1) representing the monaural sound signal of the        other voice source point are output. From the two monaural codes        CFM_(M1) and CMM_(N1) output by the multipoint control unit 100,        each fixed communication terminal apparatus 200-m _(else) that        is not the voice source point obtains, by performing the process        of the above-described case B, decoded sound signals of two        channels that are sound signals corresponding to the monaural        sound signals of the two voice source points in which paired        coding and decoding are not connected in tandem. The sound        signals corresponding to the monaural sound signals of the two        voice source points are a sound signal corresponding to a sound        signal in which the sound signal of the two-channel stereo of        one voice source point is mixed, and a sound signal        corresponding to the monaural sound signal of another voice        source point.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n _(else) that is not the        voice source point, the monaural code CTM_(M1N1) representing        one sound signal obtained by mixing, and then coding, sound        signals obtained by decoding the monaural codes CFM_(M1) and        CMM_(N1) of the two voice source points. From one monaural code        CTM_(M1N1) output from the multipoint control unit 100, each        mobile communication terminal apparatus 300-n _(else) that is        not the voice source point obtains one decoded sound signal that        is a monaural sound signal in which all sound signals of the two        voice source points are mixed, and paired coding and decoding        are connected in tandem mixed sound signal.        Case Where Mobile Communication Terminal Apparatus 300-N₁ (N₁ is        any one of integers from 1 to N) and Mobile Communication        Terminal Apparatus 300-N₂ (N₂ is any one of integers from 1 to N        and is different from N₁) are Selected

In the above-described example in which the power of the sound signal isused as the selection criterion, this case corresponds to a case wherean apparatus whose power of the sound signal is largest and an apparatuswhose power is second largest and is equal to or greater than athreshold in M+N terminal apparatuses are the mobile communicationterminal apparatus 300-N₁ (N₁ is any one of integers from 1 to N) andthe mobile communication terminal apparatus 300-N₂ (N₂ is any one ofintegers from 1 to N and is different from N₁).

In this case, the point selection section 110 of the multipoint controlunit 100 outputs the selection point information of the above-describedcase 5, and the bit stream generation section 120 of the multipointcontrol unit 100 performs the operation of the above-described “CaseWhere Selection Point Information is Information of Case 5”, andtherefore, the multipoint phone connection system 10 operates in thefollowing manner, which includes subsequent operations of each terminalapparatus.

-   -   The multipoint control unit 100 outputs, to the mobile        communication terminal apparatus 300-N₁, the monaural code        CMM_(N2) representing a monaural sound signal picked up by the        mobile communication terminal apparatus 300-N₂. From one        monaural code CMM_(N2) output by the multipoint control unit        100, the mobile communication terminal apparatus 300-N₁ obtains        a monaural decoded sound signal corresponding to a monaural        sound signal picked up by the mobile communication terminal        apparatus 300-N₂.    -   The multipoint control unit 100 outputs, to the mobile        communication terminal apparatus 300-N₂, the monaural code        CMM_(N1) representing a monaural sound signal picked up by the        mobile communication terminal apparatus 300-N₁. From one        monaural code CMM_(N1) output by the multipoint control unit        100, the mobile communication terminal apparatus 300-N₂ obtains        a monaural decoded sound signal corresponding to the monaural        sound signal picked up by the mobile communication terminal        apparatus 300-N₁.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n _(else) (n_(else) is an        integer from 1 to N and is different from both N₁ and N₂) that        is neither the mobile communication terminal apparatus 300-N₁        nor the mobile communication terminal apparatus 300-N₂, the        monaural code CMM_(N1N2) obtained by mixing, and then coding a        sound signal obtained by decoding the monaural code CMM_(N1)        representing a monaural sound signal picked up by the mobile        communication terminal apparatus 300-N₁ and a sound signal        obtained by decoding the monaural code CMM_(N2) representing a        monaural sound signal picked up by the mobile communication        terminal apparatus 300-N₂. From one monaural code CMM_(N1N2)        output by the multipoint control unit 100, each mobile        communication terminal apparatus 300-n _(else) obtains one        monaural decoded sound signal corresponding to a mixed sound        signal of a monaural sound signal picked up by the mobile        communication terminal apparatus 300-N₁ and a monaural sound        signal picked up by the mobile communication terminal apparatus        300-N₂.    -   The multipoint control unit 100 outputs, to each fixed        communication terminal apparatus 200-m (m is an integer from 1        to M), the monaural code CMM_(N)i representing a monaural sound        signal picked up by the mobile communication terminal apparatus        300-N₁ and the monaural code CMM_(N2) representing a monaural        sound signal picked up by the mobile communication terminal        apparatus 300-N₂. From the two monaural codes CMM_(N1) and        CMM_(N2) output by the multipoint control unit 100, each fixed        communication terminal apparatus 200-m obtains, by performing        the process of the above-described case B, decoded sound signals        of two channels, namely, a sound signal corresponding to a        monaural sound signal picked up by the mobile communication        terminal apparatus 300-N₁, and a sound signal corresponding to a        monaural sound signal picked up by the mobile communication        terminal apparatus 300-N₂.

Note that in an example of a voice conference, this case corresponds toa frame in which the two points, the mobile communication terminalapparatus 300-N₁ and the mobile communication terminal apparatus 300-N₂,are the voice source points, and the multipoint phone connection system10 operates as follows.

-   -   The multipoint control unit 100 outputs, to the mobile        communication terminal apparatus 300-N₁ and the mobile        communication terminal apparatus 300-N₂ of the voice source        points, a monaural code CMM_(Mx) (x is 1 or 2) representing the        monaural sound signal of the other voice source point. From the        one monaural code CMM_(Mx) output by the multipoint control unit        100, each of the mobile communication terminal apparatus 300-N₁        and the mobile communication terminal apparatus 300-N₂ of the        voice source points obtains a monaural decoded sound signal that        is a sound signal corresponding to the monaural sound signal of        the other voice source point in which paired coding and decoding        are not connected in tandem.    -   The multipoint control unit 100 outputs, to each mobile        communication terminal apparatus 300-n _(else) that is not the        voice source point, the monaural code CTM_(M1M2) representing        one sound signal obtained by mixing and coding sound signals        obtained by decoding the monaural codes CMM_(M1) and CMM_(M2)        representing the monaural sound signals of the two voice source        points.

From one monaural code CTM_(M1M2) output by the multipoint control unit100, each mobile communication terminal apparatus 300-n _(else) that isnot the voice source point obtains one decoded sound signal that is amonaural sound signal in which all sound signals of the two voice sourcepoints are mixed, and paired coding and decoding are connected in tandemmixed sound signal.

-   -   The multipoint control unit 100 outputs, to each fixed        communication terminal apparatus 200-m, the two monaural codes        CMM_(M1) and CMM_(M2) representing the monaural sound signals of        the two voice source points. From the two monaural codes        CMM_(M1) and CMM_(M2) output by the multipoint control unit 100,        each fixed communication terminal apparatus 200-m obtains, by        performing the process of the above-described case B, decoded        sound signals of two channels that are two monaural sound        signals corresponding to the monaural sound signals of the two        voice source points in which paired coding and decoding are not        connected in tandem.

SECOND EMBODIMENT

While the coding section of the fixed communication terminal apparatusaccording to the first embodiment obtains, as an extension code, a codethat cannot obtain any of decoded digital sound signals of two channelswhen using only the extension code, but can obtain both of the decodeddigital sound signals of the two channels when used together with amonaural code, the extension code may be obtained as a code that canobtain both of the decoded digital sound signals of the two channelseven when only the extension code is used without using a monaural code.This aspect is described as a second embodiment.

The configuration of the multipoint phone connection system 10 accordingto the second embodiment and the configuration of each apparatusincluded in the multipoint phone connection system 10 according to thesecond embodiment are same as the configuration of the multipoint phoneconnection system 10 according to the first embodiment and eachapparatus included in the multipoint phone connection system 10according to the first embodiment. The second embodiment differs fromthe first embodiment in the operations of the coding section 212-m ofthe sound signal fixed transmission side unit 210-m of the fixedcommunication terminal apparatus 200-m and the decoding section 222-m ofthe sound signal fixed reception side unit 220-m of the fixedcommunication terminal apparatus 200-m, and therefore the differencesbetween the second embodiment and the first embodiment are describedbelow.

Coding Section 212-m

For each frame, the coding section 212-m according to the secondembodiment obtains a monaural code by coding a mixed signal of digitalsound signals of two channels input from the sound pickup section 211-mby the above-described first coding scheme, and obtains an extensioncode by stereo-coding the input digital sound signals of two channels bya predetermined third coding scheme, and, outputs the obtained monauralcode and the obtained extension code to the control information grantingsection 213-m.

As the third coding scheme, the same coding scheme is used in the codingsections 212-m of all sound signal fixed transmission side units 210-m.As the third coding scheme, it is necessary to use a coding scheme inwhich the bit rate of the extension code is equal to or smaller than avalue obtained by subtracting the bit rate of the monaural code from thecommunication capacity of the fixed transmission path 400-m. As thethird coding scheme, as long as the bit rate of the extension codesatisfies the above-described condition, it is possible to use a codingscheme capable of efficiently coding sound signals of two channels so asto obtain, as an extension code, a code that can obtain both of decodeddigital sound signals of two channels even when only the extension codeis used without using a monaural code obtained by the first codingscheme. Naturally, as the third coding scheme, a scheme that codes eachof sound signals of two channels by the above-described first codingscheme may be used, and each of sound signals of two channels may becoded by the above-described 13.2 kbps mode of the 3GPP EVS standard,for example.

Decoding Section 222-m

As in the decoding section 222-m according to the first embodiment, whenthere is an input code on the basis of the input code information, thedecoding section 222-m according to the second embodiment obtains, foreach frame, one or two decoded digital sound signals by decoding theinput code and outputs the one or two signals to the playback section223-m. It should be noted that, the decoding section 222-m according tothe second embodiment performs a process of a case A′ described belowinstead of the above-described case A of the decoding section 222-maccording to the first embodiment.

Case A′

When the input code information is “information representing that a codeincluded in a code string representing a sound signal is a pair of amonaural code and an extension code”, the decoding section 222-maccording to the second embodiment obtains two decoded digital soundsignals by decoding the input extension code by a predetermined thirddecoding scheme, and outputs the signals. That is, the decoding section222-m obtains the two decoded digital sound signals by decoding only theextension code without decoding the monaural code, and outputs thesignals. Note that as the third decoding scheme, the decoding section222-m according to the second embodiment uses a decoding schemecorresponding to the third coding scheme used in the coding section212-m of the sound signal fixed transmission side unit 210-m accordingto the second embodiment.

Modification 1 of Second Embodiment

In the decoding section of the fixed communication terminal apparatusaccording to the second embodiment, the monaural code is not used in thecase of the above-described case A′. Thus, in this case, the controlinformation analysis section of the fixed communication terminalapparatus may not output the monaural code. The following describes adifference between the second embodiment and this aspect as Modification1 of the second embodiment.

Control Information Analysis Section 221-m

When the code information represented by the control code included inthe input bit stream for a fixed terminal is “information representingthat a code included in a code string representing a sound signal is apair of a monaural code and an extension code”, the control informationanalysis section 221-m of Modification 1 of the second embodimentoutputs code information represented by the control code included in theinput bit stream for a fixed terminal, and an extension code of a coderepresenting a sound signal included in the input bit stream for a fixedterminal. In the case other than the above-mentioned case, that is, whenthe code information represented by the control code included in theinput bit stream for a fixed terminal is information other than“information representing that a code included in a code stringrepresenting a sound signal is a pair of a monaural code and anextension code”, the control information analysis section 221-m ofModification 1 of the second embodiment performs the same operation asthe control information analysis section 221-m according to the secondembodiment.

Modification 2 of Second Embodiment

In the decoding section of the fixed communication terminal apparatusaccording to the second embodiment, the monaural code is not used in thecase of the above-described case A′. Thus, in this case, the bit streamgeneration section of the multipoint control unit may not output themonaural code. The following describes a difference between the secondembodiment and this aspect as Modification 2 of the second embodiment.

Bit stream Generation Section 120

On the basis of the input selection point information, the bit streamgeneration section 120 of Modification 2 of the second embodimentgenerates, for each frame, a bit stream for a fixed terminal to beoutput to each fixed communication terminal apparatus 200-m and a bitstream for a mobile terminal to be output to each mobile communicationterminal apparatus 300-n by using the input fixed terminal sending bitstream and the input mobile terminal sending bit stream, and outputs thebit stream, as with the bit stream generation section 120 according tothe second embodiment. It should be noted that when the selection pointinformation is information named “Fix-M₁”, the bit stream generationsection 120 of Modification 2 of the second embodiment generates, foreach fixed communication terminal apparatus 200-m _(else) (m_(else) isan integer from 1 to M and is different from M₁) other than the fixedcommunication terminal apparatus 200-M₁, a bit stream for a fixedterminal including only the extension code CFE_(M1) included in thefixed terminal sending bit stream output by the fixed communicationterminal apparatus 200-M₁ as a code representing a sound signal and acontrol code representing that the code information is “informationrepresenting that a code included in a code string representing a soundsignal is one extension code”, and outputs the bit stream to each fixedtransmission path 400-m _(else) to which each fixed communicationterminal apparatus 200-m _(else) is connected.

Control Information Analysis Section 221-m

When the code information represented by the control code included inthe input bit stream for a fixed terminal is “information representingthat a code included in a code string representing a sound signal is oneextension code”, the control information analysis section 221-m ofModification 2 of the second embodiment outputs code informationrepresented by the control code included in the input bit stream for afixed terminal, and one extension code that is a code representing asound signal included in the input bit stream for a fixed terminal. Inthe case other than the above-mentioned case, that is, when the codeinformation represented by the control code included in the input bitstream for a fixed terminal is information other than “informationrepresenting that a code included in a code string representing a soundsignal is one extension code”, the control information analysis section221-m of Modification 2 of the second embodiment performs the sameoperation as the control information analysis section 221-m according tothe second embodiment.

Decoding Section 222-m

When the input code information is “information representing that a codeincluded in a code string representing a sound signal is one extensioncode”, the decoding section 222-m of Modification 2 of the secondembodiment obtains two decoded digital sound signals by decoding theinput extension code by the above-described third decoding scheme, andoutputs the signals. In the case other than the above-mentioned case,that is, when the input code information is information other than“information representing that a code included in a code stringrepresenting a sound signal is one extension code”, the decoding section222-m of Modification 2 of the second embodiment performs the sameoperation as the decoding section 222-m according to the secondembodiment.

THIRD EMBODIMENT

In the first embodiment, the extension code obtained by the codingsection of the fixed communication terminal apparatus is a code thatcannot obtain any of decoded digital sound signals of two channels whenusing only the extension code, but can obtain both of the decodeddigital sound signals of the two channels when used together with amonaural code, whereas in the second embodiment, the code is a code thatcan obtain both of decoded digital sound signals of two channels evenwhen only the extension code is used without using a monaural code.Here, one of the extension code according to the first embodiment andthe extension code according to the second embodiment may be selectedfor each frame. This aspect is described as the third embodiment.

The configuration of the multipoint phone connection system 10 accordingto the third embodiment and the configuration of each apparatus includedin the multipoint phone connection system 10 according to the thirdembodiment are the same as the configuration of the multipoint phoneconnection system 10 and each apparatus included in the multipoint phoneconnection system 10 according to the first embodiment and the secondembodiment. The differences between the third embodiment and the firstembodiment are described below.

Coding Section 212-m

For each frame, the coding section 212-m according to the thirdembodiment obtains a monaural code by coding a mixed signal of digitalsound signals of two channels input from the sound pickup section 211-mby the above-described first coding scheme, and outputs the obtainedmonaural code to the control information granting section 213-m of thesound signal fixed transmission side unit 210-m as in the coding section212-m according to the first embodiment and the second embodiment.

In addition, the coding section 212-m according to the third embodimentoutputs, to the control information granting section 213-m of the soundsignal fixed transmission side unit 210-m, an extension code including acode representing information corresponding to a difference betweeninput digital sound signals of two channels, or an extension codeobtained by stereo-coding an input digital sound signals of two channelsby the above-described third coding scheme.

For example, the coding section 212-m according to the third embodimentobtains a monaural code by coding a mixed signal of the input digitalsound signals of two channels by the above-described first codingscheme, and obtains a provisional decoded digital sound signal bydecoding the monaural code by the first decoding scheme, and, obtains afirst provisional extension code by coding the information correspondingto a difference between the input digital sound signals of two channelsby the above-described second coding scheme, obtains decodinginformation corresponding to the difference by decoding the firstprovisional extension code by the second decoding scheme, and, with theprovisional decoded digital sound signal and the decoding informationcorresponding to the difference, obtains first provisional decodeddigital sound signals of two channels by regarding the provisionaldecoded digital sound signal as a mixed signal of the first decodeddigital sound signals of two channels, and regarding the decodinginformation corresponding to the difference as information correspondingto the difference between the first provisional decoded digital soundsignals of two channels to thereby obtain first provisional decodeddigital sound signals of two channels.

In addition, the coding section 212-m obtains a second provisionalextension code by coding digital sound signals of two channels by theabove-described third coding scheme, and obtains a second provisionaldecoded digital sound signals of two channels by decoding the obtainedsecond provisional extension code by the third decoding scheme. Then,the coding section 212-m outputs, as an extension code, a provisionalextension code corresponding to the smaller of coding distortiondetermined by the input digital sound signals of two channels and thefirst provisional decoded digital sound signals of two channels, andcoding distortion determined by the input digital sound signals of twochannels and the second provisional decoded digital sound signals of twochannels. In addition, for example, by obtaining an estimated value ofthe coding distortion of the first provisional decoded digital soundsignal as first estimated coding distortion, and obtaining an estimatedvalue of the coding distortion of the second provisional decoded digitalsound signal as second estimated coding distortion, the coding section212-m according to the third embodiment obtains an extension code byperforming a coding process on the smaller of the first estimated codingdistortion and the second estimated coding distortion, and outputs theextension code.

In addition, for example, by obtaining the first provisional extensioncode by coding the information corresponding to a difference between theinput digital sound signals of two channels by the above-describedsecond coding scheme, and obtaining the second provisional extensioncode by stereo-coding the input digital sound signals of two channels bythe above-described third coding scheme, the coding section 212-maccording to the third embodiment selects one of the first provisionalextension code and the second provisional extension code that has asmaller code amount, and outputs the selected code as an extension code.In addition, for example, by obtaining, as a first estimated codeamount, the estimated value of the code amount of the extension codeobtained by coding the information corresponding to a difference betweenthe input digital sound signals of two channels by the above-describedsecond coding scheme, and obtaining, as a second estimated code amount,the estimated value of the code amount of the extension code obtained bystereo-coding the input digital sound signals of two channels by theabove-described third coding scheme, the coding section 212-m accordingto the third embodiment obtains an extension code by performing a codingprocess on the smaller of the first estimated code amount and the secondestimated code amount, and outputs the extension code.

In addition, for example, the coding section 212-m according to thethird embodiment operates to obtain an extension code including a coderepresenting information corresponding to a difference between the inputdigital sound signals of two channels in accordance with a result ofanalyzation of the input digital sound signals of two channels, orobtain an extension code by stereo-coding the input digital soundsignals of two channels by the above-described third coding scheme, andoutputs the obtained extension code. In addition, for example, under thecontrol of a control section (not illustrated) of the fixedcommunication terminal apparatus 200-m, the coding section 212-maccording to the third embodiment operates to obtain an extension codeincluding the code representing information corresponding to adifference between the input digital sound signals of two channels, orobtain an extension code by stereo-coding the input digital soundsignals of two channels by the above-described third coding scheme, andoutputs the obtained extension code.

Further, the coding section 212-m according to the third embodimentobtains information that identifies whether the output extension code isan extension code including a code representing informationcorresponding to a difference between the input digital sound signals oftwo channels, or an extension code obtained by stereo-coding the inputdigital sound signals of two channels by the above-described thirdcoding scheme, and outputs the information to the control informationgranting section 213-m.

Control Information Granting Section 213-m

When a code representing a sound signal is a monaural code and anextension code, the control information granting section 213-m of thirdembodiment outputs control code representing code information includingnot only “information representing that a code included in a code stringrepresenting a sound signal is a pair of a monaural code and anextension code”, but also information that identifies which of theabove-described extension codes is the extension code, that is,“information that identifies whether the extension code is an extensioncode including a code representing information corresponding todifference, or is an extension code obtained by the third codingscheme”.

Decoding Section 222-m

The decoding section 222-m according to the third embodiment performsthe process of the above-described case A of the decoding section 222-maccording to the first embodiment in a case where the input codeinformation is “information representing that a code included in a codestring representing a sound signal is a pair of a monaural code and anextension code”, and the “information that identifies whether theextension code is an extension code including a code representinginformation corresponding to difference, or is an extension codeobtained by the third coding scheme” or performs the process of theabove-described case A′ of the decoding section 222-m according to thesecond embodiment in a case where the input code information is“information representing that a code included in a code stringrepresenting a sound signal is a pair of a monaural code and anextension code”, and “information that identifies whether the extensioncode is an extension code including a code representing informationcorresponding to difference, or is an extension code obtained by thethird coding scheme”.

In other cases, that is, when the input code information is informationother than “information representing that a code included in a codestring representing a sound signal is a pair of a monaural code and anextension code”, the decoding section 222-m according to the thirdembodiment operates as with the decoding section 222-m according to thefirst embodiment and the second embodiment.

Note that the third embodiment may be modified as with Modification 1 orModification 2 of the second embodiment.

OTHER EMBODIMENTS Number of Terminal Apparatuses in Configuration inWhich Point Selection Section Selects up to Two Points

For the sake of simplicity of description, the above-mentionedembodiments are described with an example in which the multipoint phoneconnection system includes two or more fixed communication terminalapparatuses and two or more mobile communication terminal apparatuses.However, the number of the terminal apparatuses included in themultipoint phone connection system according to the above-mentionedembodiments is not limited thereto, and it suffices that the multipointphone connection system according to the above-mentioned embodimentsincludes one or more fixed communication terminal apparatuses and one ormore mobile communication terminal apparatuses such that the totalnumber of fixed communication terminal apparatuses and mobilecommunication terminal apparatuses is three or more. That is, itsuffices in the multipoint phone connection system of theabove-mentioned embodiments, M≥1, N≥1, and M+N≥3.

It should be noted that, when M is 1, that is, when the multipoint phoneconnection system includes one fixed communication terminal apparatusand two or more mobile communication terminal apparatuses, no two pointsselected by the point selection section 110 of the multipoint controlunit 100 can be both fixed communication terminal apparatuses. Thus, thepoint selection information output by the point selection section 110cannot be the case 3, and the point selection information output by thepoint selection section 110 is any of the cases 1, 2, 4 and 5. Inaddition, in this case, when the fixed communication terminal apparatusis included in the points selected by the point selection section 110,the points that are not selected by the point selection section 110cannot include the fixed communication terminal apparatus, and so thebit stream generation section 120 of the multipoint control unit 100cannot output the bit stream of the second pattern when the pointselection information is the information of the case 1, and cannotoutput the bit stream of the third pattern when the point selectioninformation is the information of the case 4, whereas the bit streamgeneration section 120 outputs the bit streams of the first pattern andthe third pattern when the point selection information is theinformation of the case 1, and outputs the bit streams of the first,second and fourth patterns when the point selection information is theinformation of the case 4. In addition, in this case, a decoding section222-1 of a sound signal fixed reception side unit 220-1 of the fixedcommunication terminal apparatus 200-1 cannot perform the process of theabove-described case A, but the decoding section 222-1 performs theprocess of any of the cases B to D.

In addition, when N is 1, that is, when the multipoint phone connectionsystem includes two or more fixed communication terminal apparatuses andone mobile communication terminal apparatus, no two points selected bythe point selection section 110 of the multipoint control unit 100 canbe both mobile communication terminal apparatuses. Thus, the pointselection information output by the point selection section 110 cannotbe the case 5, and the point selection information output by the pointselection section 110 is any of the cases 1 to 4. In addition, in thiscase, when the mobile communication terminal apparatus is included inthe points selected by the point selection section 110, the points thatare not selected by the point selection section 110 cannot include themobile communication terminal apparatus, and so the bit streamgeneration section 120 of the multipoint control unit 100 cannot outputthe bit stream of the second pattern when the point selectioninformation is the information of the case 2, and cannot output the bitstream of the fourth pattern when the point selection information is theinformation of the case 4, and outputs the bit streams of the firstpattern and the third pattern when the point selection information isthe information of the case 2, and outputs the bit streams of the firstpattern, the second pattern and the third pattern when the pointselection information is the information of the case 4.

Number of Points Selected by Point Selection Section

In addition, for the sake of simplicity of description, theabove-mentioned embodiments are described with an example in which thepoint selection section 110 of the multipoint control unit 100 selectsone or two points. However, the number of points selected by the pointselection section 110 is not limited thereto, and three or more pointsmay be selected as long as the monaural code obtained by theabove-described first coding scheme falls within a range of thecommunication capacity for real-time transmission through thetransmission path for a voice line of a fixed phone. That is, itsuffices that the point selection section 110 of the multipoint controlunit 100 selects up to K (K is an integer of 2 or greater) points. Inthis case, the bit stream generation section 120 of the multipointcontrol unit 100, each fixed communication terminal apparatus 200-m, andeach mobile communication terminal apparatus 300-n operate as follows.

Communication Terminal Apparatus Having a Value of 0 for the Number ofSelected Points Other than the Point of the Communication TerminalApparatus itself, and Operation of Bit stream Generation Section forthat Communication Terminal Apparatus

When the number of selected points is one (i.e., K is 1), the terminalapparatus of the selected point has a value of 0 for the number ofselected points other than the point of the terminal apparatus itself.The bit stream generation section 120 of the multipoint control unit 100does not output a code string representing a sound signal to thecommunication terminal apparatus having a value of 0 for the number ofselected points other than the point of the communication terminalapparatus itself as described above in the first embodiment. Thecommunication terminal apparatus having a value of 0 for the number ofselected points other than the point of the communication terminalapparatus itself does not decode a code string representing a soundsignal, and does not obtain a decoded sound signal as described above inthe first embodiment.

Fixed Communication Terminal Apparatus Having a Value of 1 for theNumber of Selected Points Other than the Point of Fixed CommunicationTerminal Apparatus itself, and Operation of Bit stream GenerationSection for that Fixed Communication Terminal Apparatus When the numberof the selected points is two (i.e., K is 2), the terminal apparatus ofeach selected point has a value of 1 for the number of selected pointsother than the point of terminal apparatus itself. In addition, when thenumber of selected points is one (i.e., K is 1), the terminal apparatusof each unselected point has a value of 1 for the number of selectedpoints other than the unselected point itself.

The bit stream generation section 120 of the multipoint control unit 100generates and outputs the bit stream including, at least a monaural codeof the selected point as a code representing a sound signal for thefixed communication terminal apparatus having a value of 1 for thenumber of selected points other than the point of the terminal apparatusitself as described above in the first embodiment, and, including theextension code of the selected point as a code representing a soundsignal when there is an extension code of the selected point.

Specifically, to the fixed communication terminal apparatus having avalue of 1 for the number of selected points other than the point of theterminal apparatus itself, the bit stream generation section 120 of themultipoint control unit 100 generates and outputs a bit stream includinga monaural code and an extension code of the selected point as a coderepresenting a sound signal when the selected point is a fixedcommunication terminal apparatus, and generates and outputs a bit streamincluding a monaural code of the selected point as a code representing asound signal when the selected point is a mobile communication terminalapparatus. The decoding section of the fixed communication terminalapparatus having a value of 1 for the number of selected points otherthan the point of the terminal apparatus itself obtains a decoded soundsignal of the selected point by decoding a monaural code of the selectedpoint, and decoding an extension code of the selected point when thereis an extension code of the selected point as described above in thefirst embodiment.

Mobile Communication Terminal Apparatus Having a Value of 1 for theNumber of Selected Points Other than the Point of the MobileCommunication Terminal Apparatus itself, and Operation of Bit streamGeneration Section for that Mobile Communication Terminal Apparatus

When the number of the selected points is two (i.e., K is 2), theterminal apparatus of each selected point has a value of 1 for thenumber of selected points other than the point of terminal apparatusitself. In addition, when the number of selected points is one (i.e., Kis 1), the terminal apparatus of each unselected point has a value of 1for the number of selected points other than the unselected pointitself. The bit stream generation section 120 of the multipoint controlunit 100 generates and outputs, to the mobile communication terminalapparatus having a value of 1 for the number of selected points otherthan the point of the mobile communication terminal apparatus itself, abit stream including a monaural code of the selected point as a coderepresenting a sound signal as described above in the first embodiment.The decoding section of the mobile communication terminal apparatushaving a value of 1 for the number of selected points other than thepoint of the mobile communication terminal apparatus itself obtains adecoded sound signal of the selected point by decoding a monaural codeof the selected point as described above in the first embodiment.

Fixed Communication Terminal Apparatus Having a value of 2 or more forthe Number of the Fixed Communication Terminal Apparatus itself, andOperation of Bit stream Generation Section for that Fixed CommunicationTerminal Apparatus

When the number of the selected points is three or more (i.e., K isequal to or greater than 3), the terminal apparatus of each selectedpoint has a value of 2 or more for the number of selected points otherthan the point of the terminal apparatus itself. In addition, when thenumber of the selected points is two or more (i.e., K is equal to orgreater than 2), the terminal apparatus of each unselected point has avalue of 2 or more for the number of selected points other than theunselected point itself. The bit stream generation section 120 of themultipoint control unit 100 generates and outputs, to the fixedcommunication terminal apparatus where the number of selected pointsother than the own point is two or more, a bit stream for a fixedterminal including k monaural codes included in sending bit streamsoutput by the two or more (k, which is an integer from 2 to K) selectedcommunication terminal apparatuses as codes representing a sound signal,and a control code representing that the code information is“information representing that a code included in a code stringrepresenting a sound signal is k monaural codes”. The controlinformation analysis section of the sound signal fixed reception sideunit of the fixed communication terminal apparatus having a value of 2or more for the number of selected points other than the point of thefixed communication terminal apparatus itself outputs, to the decodingsection, code information that is “information representing that a codeincluded in a code string representing a sound signal is k monauralcodes” and k monaural codes. The decoding section of the sound signalfixed reception side unit of the fixed communication terminal apparatushaving a value of 2 or more for the number of selected points other thanthe point of the fixed communication terminal apparatus itself obtains kdecoded digital sound signals by decoding each of the input k monauralcodes by the above-described first decoding scheme, and outputs thesignals. Note that the playback section of the sound signal fixedreception side unit of each fixed communication terminal apparatus mayinclude up to K DA conversion sections and up to K speakers.

Mobile Communication Terminal Apparatus Having a Value of 2 or more forthe Number of Selected Points Other than the Point of the MobileCommunication Terminal Apparatus itself, and Operation of Bit streamGeneration Section for that Mobile Communication Terminal Apparatus

When the number of the selected points is three or more (i.e., K isequal to or greater than 3), the terminal apparatus of each selectedpoint has a value of 2 or more for the number of selected points otherthan the point of the terminal apparatus itself. In addition, when thenumber of the selected points is two or more (i.e., K is equal to orgreater than 2), the terminal apparatus of each unselected point has avalue of 2 or more for the number of selected points other than theunselected point itself.

For the mobile communication terminal apparatus having a value of 2 ormore for the number of selected points other than the mobilecommunication terminal apparatus itself, the bit stream generationsection 120 of the multipoint control unit 100 obtains k decoded digitalsound signals by decoding each monaural code included in bit streamsoutput by the two or more (k, which is an integer from 2 to K) selectedcommunication terminal apparatuses, and obtains a mixed digital soundsignal by mixing the obtained k decoded digital sound signals obtains amonaural code by coding the mixed digital sound signal by theabove-described first coding scheme, and generates and outputs a bitstream for a mobile terminal including the one monaural code obtainedfrom the mixed digital sound signal as a code representing a soundsignal. The decoding section of the mobile communication terminalapparatus having a value of 2 or more for

the number of selected points other than the mobile communicationterminal apparatus itself obtains one decoded digital sound signal bydecoding the one monaural code by the above-described first decodingscheme, and outputs the signal.

Number of Terminal Apparatuses in Configuration in which Point SelectionSection Selects K Points

As is clear from the above two descriptions, it suffices that when K (Kis an integer of 2 or greater) is set as the number with which themonaural code obtained by the above-described first coding scheme fallswithin the range of the communication capacity for real-timetransmission through the transmission path for a voice line of a fixedphone, the multipoint phone connection system has a configuration inwhich the point selection section 110 of the multipoint control unit 100selects up to K points, including one or more fixed communicationterminal apparatuses and one or more mobile communication terminalapparatuses such that the total number of fixed communication terminalapparatuses and mobile communication terminal apparatuses is K+1 ormore. That is, it suffices that in the multipoint phone connectionsystem of the above-mentioned embodiments, M≥1, N≥1, and M+N≥K+1.

Number of Channels of Sound Signal of Fixed Communication TerminalApparatus

In addition, for the sake of simplicity of description, theabove-mentioned embodiments are described with an example in which thesound signal fixed transmission side unit 210-m of the fixedcommunication terminal apparatus 200-m obtains and outputs a bit streamincluding a code corresponding to digital sound signals of two channels.However, the number of channels is not limited thereto as long as two ormore channels are provided. When the number of channels is set to C (Cis an integer of 2 or greater), in this case, it suffices that the soundpickup section 211-m of the sound signal fixed transmission side unit210-m of the fixed communication terminal apparatus 200-m includes Cmicrophones and C AD conversion sections, and it suffices that, for eachframe, the coding section 212-m of the sound signal fixed transmissionside unit 210-m of the fixed communication terminal apparatus 200-mobtains a monaural code by coding a mixed signal of digital soundsignals of C channels input from the sound pickup section 211-m by thepredetermined first coding scheme, and obtains an extension codeincluding a code representing information corresponding to a differencebetween the input digital sound signals of C channels. It suffices that,in this case, instead of the above-described case A, the decodingsection 222-m of the sound signal fixed reception side unit 220-m of thefixed communication terminal apparatus 200-m obtains a provisionaldecoded digital sound signal by decoding the input monaural code by thepredetermined first decoding scheme, and obtains decoded differenceinformation from a code representing information corresponding to adifference included in the input extension code, then obtains, from theobtained provisional decoded digital sound signal and the obtaineddecoded difference information, C decoded digital sound signals byregarding the provisional decoded digital sound signal as C decodeddigital sound signals mixed signal, and regarding the decoded differenceinformation as information corresponding to the difference between Cdecoded digital sound signals and outputs the C decoded digital soundsignals. In addition, when the input extension code includes not only adifference code that is a code representing information corresponding tothe difference, but also an error code, it suffices that the decodingsection 222-m further obtains decoded error information from an errorcode included in the input extension code, obtains C decoded digitalsound signals, from the provisional decoded digital sound signal, thedecoded error information and the decoded difference information, byregarding the provisional decoded digital sound signal as a mixed signalof C decoded sound signals, regarding the decoded error information asinformation corresponding to an error of the provisional decoded digitalsound signal, and regarding the decoded difference information asinformation corresponding to the difference between C decoded digitalsound signals and outputs the C decoded digital sound signals. Inaddition, in the above-mentioned cases, the playback section 223-m ofthe sound signal fixed reception side unit 220-m of the fixedcommunication terminal apparatus 200-m may include up to C DA conversionsections and up to C speakers. Note that when coding the informationcorresponding to a difference between the input digital sound signals ofC channels, the coding section 212-m obtains a code representinginformation corresponding to the difference by coding informationcorresponding to the difference between channels of input digital soundsignals of C channels by the predetermined second coding scheme, andincludes the code in the extension code so that the decoding section222-m may obtain decoded difference information by decoding the coderepresenting the information corresponding to the difference included inthe input extension code by the predetermined second decoding scheme. Asthe second decoding scheme and the second coding scheme, a multichanneldecoding scheme (ISO/IEC 14496-3 11.6.8.1.2) of MPEG-4 ALS standard anda processing technique used in a coding scheme corresponding to thatscheme may be used, for example Note that the information correspondingto a difference between channels of digital sound signals of C channelsis waveform information representing a difference between digital soundsignals of C channels, a feature parameter representing a differencebetween digital sound signals of C channels or the like as in theabove-described first embodiment.

Program and Recording Medium

The process of each section of the first communication network terminalapparatus 200-m, the second communication network terminal apparatus300-n, and the multipoint control unit 100 may be implemented by acomputer. In other words, the process of each step of a coding methodthat is a coding side method corresponding to the first communicationnetwork terminal apparatus 200-m, and a decoding method that is adecoding side method corresponding to the first communication networkterminal apparatus 200-m may be implemented by a computer. In addition,the process of each step of the method corresponding to the secondcommunication network terminal apparatus 300-n may be implemented by acomputer. In addition, the process of each step of the multipointcontrol method corresponding to the multipoint control unit 100 may beimplemented by a computer. In this case, the process of each step isdescribed by a program. Then, by implementing this program by acomputer, the process of each step is implemented by the computer.

Each program in which the processing details are described may berecorded in a computer-readable recording medium. The computer-readablerecording medium can be any type of medium such as a magnetic recordingdevice, an optical disc, a magneto-optical recording medium, or asemiconductor memory.

The processing of each part may be composed by causing the computer toexecute a predetermined program on the computer, or at least a part ofthe processing may be implemented in the form of hardware.

It is needless to say that the present disclosure can appropriately bemodified without departing from the gist of the present disclosure.

1. A multipoint control method in a multipoint control unit to which oneor more first communication network terminal apparatuses and one or moresecond communication network terminal apparatuses are connected througha communication path, the number of points at which the one or morefirst communication network terminal apparatuses are located being M (Mis an integer of 1 or greater), the number of points at which the one ormore second communication network terminal apparatuses are located beingN (N is an integer of 1 or greater, and M+N is 3 or greater), the methodcomprising: a point selecting step of, for a predetermined time period,selecting, by the multipoint control unit, one point or two points fromamong M points at which the one or more first communication networkterminal apparatuses are located and N points at which the one or moresecond communication network terminal apparatuses are located, a bitstream input from each first communication network terminal apparatus tothe multipoint control unit through the communication path being a bitstream including, as codes representing a sound signal, a monaural codeCFM_(m) (m is an integer from 1 to M) obtained by coding a mixed signalof sound signals of two or more channels input to the firstcommunication network terminal apparatus by a first coding scheme and anextension code CFE_(m) including a code representing informationcorresponding to a difference between the input sound signals of two ormore channels, and a bit stream input from each second communicationnetwork terminal apparatus to the multipoint control unit through thecommunication path being a bit stream including, as a code representinga sound signal, a monaural code CMM_(n) (n is an integer from 1 to N)obtained by coding a sound signal of one channel input to the secondcommunication network terminal apparatus by the first coding scheme; anda bit stream generating step of, when a single first communicationnetwork terminal apparatus of an M_(1-th) point (M₁ is an integer from 1to M) and a single second communication network terminal apparatus of anN_(1-th) point (N₁ is an integer from 1 to N) are selected from the oneor more first communication network terminal apparatuses and the one ormore second communication network terminal apparatuses, generating andoutputting, by the multipoint control unit, as a bit stream for anunselected first communication network terminal apparatus of the one ormore first communication network terminal apparatuses that is located ata points that is not selected in the point selecting step, a bit streamincluding, as codes representing a sound signal, a monaural codeCFM_(M1) of codes representing a sound signal of the M_(1-th) point anda monaural code CMM_(N1) that is a code representing a sound signal ofthe N_(1-th) point.
 2. The multipoint control method according to claim1, wherein, in the bit stream generating step, when the single firstcommunication network terminal apparatus of the M_(1-th) point and thesingle second communication network terminal apparatus of the N_(1-th)point are selected from the one or more first communication networkterminal apparatuses and the one or more second communication networkterminal apparatuses, a bit stream including, as a code representing asound signal, the monaural code CMM_(N1) that is a code representing asound signal of the N_(1-th) point is further generated and output as abit stream for the selected single first communication network terminalapparatus of the M_(1-th) point.
 3. The multipoint control methodaccording to claim 1, wherein, in the bit stream generating step, whenthe single first communication network terminal apparatus of theM_(1-th) point and the single second communication network terminalapparatus of the N_(1-th) point are selected from the one or more firstcommunication network terminal apparatuses and the one or more secondcommunication network terminal apparatuses, a bit stream including, as acode representing a sound signal, the monaural code CFM_(M1) of thecodes representing a sound signal of the M_(1-th) point is furthergenerated and output as a bit stream for the selected single secondcommunication network terminal apparatus of the N_(1-th) point.
 4. Themultipoint control method according to claim 1, wherein, in the bitstream generating step, when the single first communication networkterminal apparatus of the M_(1-th) point and the single secondcommunication network terminal apparatus of the N_(1-th) point areselected from the one or more first communication network terminalapparatuses and the one or more second communication network terminalapparatuses, a first decoded sound signal is obtained by decoding themonaural code CFM_(M1) of the codes representing a sound signal of theM_(1-th) point by a first decoding scheme corresponding to the firstcoding scheme, a second decoded sound signal is obtained by decoding themonaural code CMM_(N1) that is a code representing a sound signal of theN_(1-th) point by the first decoding scheme, a mixed sound signal isobtained by mixing the first decoded sound signal and the second decodedsound signal, a monaural code CTM_(M1N1) is obtained by coding the mixedsound signal by the first coding scheme, and a bit stream including, asa code representing a sound signal, the monaural code CTM_(M1N1)obtained from the mixed sound signal is further generated and output asa bit stream for an unselected second communication network terminalapparatus of the one or more second communication network terminalapparatuses that is located at a point that is not selected in the pointselecting step.
 5. A multipoint control unit to which one or more firstcommunication network terminal apparatuses and one or more secondcommunication network terminal apparatuses are connected through acommunication path, the number of points at which the one or more firstcommunication network terminal apparatuses are located being M (M is aninteger of 1 or greater), the number of points at which the one or moresecond communication network terminal apparatuses are located being N (Nis an integer of 1 or greater, and M+N is 3 or greater), the multipointcontrol unit comprising: processing circuitry configured to, for apredetermined time period, select one point or two points from among Mpoints at which the one or more first communication network terminalapparatuses are located and N points at which the one or more secondcommunication network terminal apparatuses are located, a bit streaminput from each first communication network terminal apparatus to themultipoint control unit through the communication path being a bitstream including, as codes representing a sound signal, a monaural codeCFM_(m) (m is an integer from 1 to M) obtained by coding a mixed signalof sound signals of two or more channels input to the firstcommunication network terminal apparatus by a first coding scheme and anextension code CFE_(m) including a code representing informationcorresponding to a difference between the input sound signals of two ormore channels, and a bit stream input from each second communicationnetwork terminal apparatus to the multipoint control unit through thecommunication path being a bit stream including, as a code representinga sound signal, a monaural code CMM_(n) (n is an integer from 1 to N)obtained by coding a sound signal of one channel input to the secondcommunication network terminal apparatus by the first coding scheme,wherein the processing circuitry is configured to, when a single firstcommunication network terminal apparatus of an M_(1-th) point (M₁ is aninteger from 1 to M) and a single second communication network terminalapparatus of an N_(1-th) point (N₁ is an integer from 1 to N) areselected from the one or more first communication network terminalapparatuses and the one or more second communication network terminalapparatuses, generate and output, as a bit stream for an unselectedfirst communication network terminal apparatus of the one or more firstcommunication network terminal apparatuses that is located at a pointthat is not selected by the processing circuitry, a bit streamincluding, as codes representing a sound signal, a monaural codeCFM_(M1) of codes representing a sound signal of the M_(1-th). point anda monaural code CMM_(N1) that is a code representing a sound signal ofthe N_(1-th) point.
 6. The multipoint control unit according to claim 5,wherein, when the single first communication network terminal apparatusof the M_(1-th) point and the single second communication networkterminal apparatus of the N_(1-th) point are selected from the one ormore first communication network terminal apparatuses and the one ormore second communication network terminal apparatuses, the processingcircuitry is configured to further generate and output a bit streamincluding, as a code representing a sound signal, the monaural codeCMM_(N1) that is a code representing a sound signal of the N_(1-th)point as a bit stream for the single selected first communicationnetwork terminal apparatus of the M_(1-th) point.
 7. The multipointcontrol unit according to claim 5, wherein, when the single firstcommunication network terminal apparatus of the M_(1-th) point and thesingle second communication network terminal apparatus of the N_(1-th)point are selected from the one or more first communication networkterminal apparatuses and the one or more second communication networkterminal apparatuses, the processing circuitry is configured to furthergenerate and output a bit stream including, as a code representing asound signal, the monaural code CFM_(M1) of the codes representing asound signal of the M_(1-th) point as a bit stream for the selectedsingle second communication network terminal apparatus of the N_(1-th)point.
 8. The multipoint control unit according to claim 5, wherein,when the single first communication network terminal apparatus of theM_(1-th) point and the single second communication network terminalapparatus of the N_(1-th) point are selected from the one or more firstcommunication network terminal apparatuses and the one or more secondcommunication network terminal apparatuses, the processing circuitry isconfigured to further obtain a first decoded sound signal by decodingthe monaural code CFM_(M1) of the codes representing a sound signal ofthe M_(1-th) point by a first decoding scheme corresponding to the firstcoding scheme, obtain a second decoded sound signal by decoding themonaural code CMM_(N1) that is a code representing a sound signal of theN_(1-th) point by the first decoding scheme, obtain a mixed sound signalby mixing the first decoded sound signal and the second decoded soundsignal, obtain a monaural code CTM_(M1N1) by coding the mixed soundsignal by the first coding scheme, and generate and output a bit streamincluding, as a code representing a sound signal, the monaural codeCTM_(M1N1) obtained from the mixed sound signal as a bit stream for anselected second communication network terminal apparatus of the one ormore second communication network terminal apparatuses that is locatedat a point that is not selected by the processing circuitry.
 9. Anon-transitory computer recording medium which stores a program whichcauses a computer to execute each step of the multipoint control methodaccording to claims 1.